Case Study: Use the Internet and Chapter 16 of the attached text, to research the murder of Dr. Martin Luther King. to answer the following questions
1. Case Summary- In a narrative format, discuss the key facts and critical issues presented in the case. Minimum word count is 500 words.
2. Case Analysis – What did the prosecution build their case upon and what evidence supported their theory against James Earl Ray?
3. Case Analysis – Discuss the advances in fingerprint evidence since Dr. King’s murder in 1968.
4. Executive Decisions – If you had been prosecuting James Earl Ray, do you feel your case would have been strong enough to win at trial? Outline your strategy.
Deadline is 7/16/2016 5pm central timezoneheadline news
The Oklahoma City Bombing
It was the biggest act of mass murder in
G
U.S. history.
On a sunny spring morning in April 1995,
O truck pulled into the parking area of the
a Ryder rental
R
Alfred P. Murrah
federal building in Oklahoma City. The
driver stepped
down from the truck’s cab and casually
D
walked O
away. Minutes later, the truck exploded into a
fireball,Nunleashing enough energy to destroy the
building and kill 168 people, including 19 children
,
and infants in the building’s day care center.
Later that morning, an Oklahoma Highway Patrol
J
officer pulled over a beat-up 1977 Mercury Marquis
E
being driven without a license plate. On further
S
investigation,
the driver, Timothy McVeigh, was
S to be in possession of a loaded firearm
found
Iand charged with transporting a firearm. At the
Cexplosion site, remnants of the Ryder truck were
A located and the truck was quickly traced to a
renter—Robert Kling, an alias for Timothy
L McVeigh. Coincidentally, the rental agreement
E and McVeigh’s driver’s license both used the
address of McVeigh’s friend, Terry Nichols.
I
Investigators later recovered McVeigh’s fingerprint
G
on a receipt for 2,000 pounds of ammonium nitrate, a basic
H
explosive ingredient. Forensic analysts also located PETN residues on the
clothing McVeigh wore on the day of his arrest. PETN is a component of detonating cord.
1 guilty of the bombing and sentenced him to die
After three days of deliberation, a jury declared McVeigh
8
by lethal injection.
7
1
B
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#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
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chapter
15
forensic investigation
of explosions
J
E
S
After studying this chapter you should
be able to:
• Understand how explosives are classifiedS
I
• List some common commercial, homemade, and military
C
explosives
A
• Describe how to collect physical evidence at the scene of an
explosion
L
• Describe laboratory procedures used to detect
and identify
explosive residues.
E
I
G
H
KEY TERMS
black powder
deflagration
detonating cord
detonation
explosion
high explosive
low explosive
oxidizing agent
primary explosive
safety fuse
secondary explosive
smokeless powder
(double-base)
smokeless powder
(single-base)
1
8
7
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Learning Objectives
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#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
374
CHAPTER 15
Explosions and Explosives
The ready accessibility of potentially explosive laboratory chemicals, dynamite, and, in some
countries, an assortment of military explosives has provided the criminal element of society with
a lethal weapon. Unfortunately for society, explosives have become an attractive weapon to criminals bent on revenge, destruction of commercial operations, or just plain mischief.
Although politically motivated bombings have received considerable publicity worldwide,
in the United States most bombing incidents are perpetrated by isolated individuals rather than by
organized terrorists. These incidents typically involve homemade explosives and incendiary
devices. The design of such weapons is limited only by the imagination and ingenuity of the
bomber.
G investigation requires close cooperation of a group of highly
Like arson investigation, bomb
specialized individuals trained andOexperienced in bomb disposal, bomb-site investigation, forensic analysis, and criminal investigation. The criminalist must detect and identify explosive chemR as well as identify the detonating mechanisms. This special
icals recovered from the crime scene
responsibility concerns us for theD
remainder of this chapter.
O
The Chemistry of Explosions
explosion
A chemical or mechanical action
caused by combustion,
accompanied by creation of heat
and rapid expansion of gases
oxidizing agent
A substance that supplies oxygen
to a chemical reaction
Like fire, an explosion is the product
N of combustion accompanied by the creation of gases and
heat. However, the distinguishing characteristic of an explosion is the rapid rate of the reaction.
,
The sudden buildup of expanding gas pressure at the origin of the explosion produces the violent
physical disruption of the surrounding environment.
Our previous discussion of the
J chemistry of fire referred only to oxidation reactions that rely
on air as the sole source of oxygen. However, we need not restrict ourselves to this type of situation. For example, explosives areE
substances that undergo a rapid exothermic oxidation reaction,
producing large quantities of gases.
SThis sudden buildup of gas pressure constitutes an explosion.
Detonation occurs so rapidly that oxygen in the air cannot participate in the reaction; thus, many
S of oxygen.
explosives must have their own source
Chemicals that supply oxygen
I are known as oxidizing agents. One such agent is found
in black powder, a low explosive, which is composed of a mixture of the following chemical
C
ingredients:
A3)
75 percent potassium nitrate (KNO
15 percent charcoal (C)
10 percent sulfur (S)
L
In this combination, oxygen containing potassium nitrate acts as an oxidizing agent for the charE
coal and sulfur fuels. As heat is applied to black powder, oxygen is liberated from potassium
I
nitrate and simultaneously combines
with charcoal and sulfur to produce heat and gases
(symbolized by 앖), as representedGin the following chemical equation:
3C HS
2KNO3
씮
carbon sulfur potassium nitrate yields
K2S
3CO2앖 1 N2앖
carbon dioxide nitrogen potassium sulfide
8
Some explosives have their oxygen and fuel components combined within one molecule. For
example, the chemical structure 7
of nitroglycerin, the major constituent of dynamite, combines
carbon, hydrogen, nitrogen, and oxygen:
1
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#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
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ƒ
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H ¬C ¬C ¬C ¬H
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NO2 NO2 NO2
FORENSIC INVESTIGATION OF EXPLOSIONS
375
When nitroglycerin detonates, large quantities of energy are released as the molecule
decomposes, and the oxygen recombines to produce large volumes of carbon dioxide, nitrogen,
and water.
Consider, for example, the effect of confining an explosive charge to a relatively small,
closed container. On detonation, the explosive almost instantaneously produces large volumes of
gases that exert enormously high pressures on the interior walls of the container. In addition, the
heat energy released by the explosion expands the gases, causing them to push on the walls with
an even greater force. If we could observe the effects of an exploding lead pipe in slow motion, we
would first see the pipe’s walls stretch and balloon under pressures as high as several hundred tons
per square inch. Finally, the walls would fragment and fly outward in all directions. This flying
debris or shrapnel constitutes a great danger to life and limb in the immediate vicinity.
On release from confinement, the gaseous products of theG
explosion suddenly expand and
compress layers of surrounding air as they move outward fromO
the origin of the explosion. This
blast effect, or outward rush of gases, at a rate that may be as high as 7,000 miles per hour creR disturb any object in its path.
ates an artificial gale that can overthrow walls, collapse roofs, and
If a bomb is sufficiently powerful, more serious damage will beD
inflicted by the blast effect than
by fragmentation debris (see Figure 15–1).
O
N
Types of Explosives
The speed at which explosives decompose varies greatly from one, to another and permits their clas-
sification as high and low explosives. In a low explosive, this speed is called the speed of
deflagration (burning). It is characterized by very rapid oxidation that produces heat, light, and a
subsonic pressure wave. In a high explosive, it is called the speedJof detonation. Detonation refers
to the creation of a supersonic shock wave within the explosive charge. This shock wave breaks the
E
chemical bonds of the explosive charge, leading to the new instantaneous
buildup of heat and gases.
S
Low explosives, such as black and smokeless powders, decompose relaS slow burning rates, they protively slowly at rates up to 1,000 meters per second. Because of their
duce a propelling or throwing action that makes them suitable as
I propellants for ammunition or
skyrockets. However, the danger of this group of explosives must not be underestimated because,
C it can explode with a force as
when any one of them is confined to a relatively small container,
lethal as that of any known explosive.
A
LOW EXPLOSIVES
© Stefan Zaklin/Corbis. All Rights
Reserved
deflagration
A very rapid oxidation reaction
accompanied by the generation of
a low-intensity pressure wave that
can disrupt the surroundings
detonation
An extremely rapid oxidation
reaction accompanied by a violent
disruptive effect and an intense,
high-speed shock wave
The most widely used explosives in the low-explosive
group are black powder and smokeless powder. The popularity of these two explosives is enhanced by their accessibility to the public. Both are available inL
any gun store, and black powder
can easily be made from ingredients purchased at any chemicalE
supply house as well.
Black powder is a relatively stable mixture of potassium nitrate or sodium nitrate, charcoal,
I
and sulfur. Unconfined, it merely burns; thus it commonly is used in safety fuses that carry a flame
to an explosive charge. A safety fuse usually consists of blackGpowder wrapped in a fabric or
plastic casing. When ignited, a sufficient length of fuse will burn at a rate slow enough to allow
H
a person adequate time to leave the site of the pending explosion. Black powder, like any other
low explosive, becomes explosive and lethal only when it is confined.
The safest and most powerful low explosive is smokeless1powder. This explosive usually
consists of nitrated cotton or nitrocellulose (single-base powder) or nitroglycerin mixed with
8 in a variety of grain sizes and
nitrocellulose (double-base powder). The powder is manufactured
shapes, depending on the desired application (see Figure 15–2).7
low explosive
The only ingredients required for a low explosive
1 are fuel and a good oxidizing
agent. The oxidizing agent potassium chlorate, for example, when mixed with sugar, produces a popB
ular and accessible explosive mix. When confined to a small container—for
example, a pipe—and
ignited, this mixture can explode with a force equivalent to a stickUof 40 percent dynamite.
Some other commonly encountered ingredients that may be combined with chlorate to
produce an explosive are carbon, sulfur, starch, phosphorus, and magnesium filings. Chlorate
mixtures may also be ignited by the heat generated from a chemical reaction. For instance,
sufficient heat can be generated to initiate combustion when concentrated sulfuric acid comes in
contact with a sugar–chlorate mix.
An explosive consisting of
nitrocellulose
Black Powder and Smokeless Powder
Chlorate Mixtures
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FIGURE 15–1
A violent explosion.
An explosive with a velocity of
detonation less than 1,000 meters
per second
black powder
Normally, a mixture of potassium
nitrate, carbon, and sulfur in the
ratio 75/15/10
safety fuse
A cord containing a core of black
powder, used to carry a flame at a
uniform rate to an explosive charge
smokeless powder
(single-base)
smokeless powder
(double-base)
An explosive consisting of a
mixture of nitrocellulose and
nitroglycerin
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
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CHAPTER 15
FIGURE 15–2
Samples of smokeless
powders.
Courtesy of ATF (Bureau of Alcohol,
Tobacco, Firearms & Explosives)
high explosive
An explosive with a velocity
of detonation greater than
1,000 meters per second
primary explosive
A high explosive that is easily
detonated by heat, shock, or
friction
secondary explosive
A high explosive that is relatively
insensitive to heat, shock, or
friction
Gas–Air Mixtures Another form of low explosive is created when a considerable quantity of natural gas escapes into a confined area and mixes with a sufficient amount of air.
If ignited, this mixture results in simultaneous combustion and sudden production of large
volumes of gases and heat. In a building, walls are forced outward by the expanding
gases, causing the roof to fall into the interiors, and objects are thrown outward and
scattered in erratic directions with no semblance of pattern.
Mixtures of air and a gaseous fuel explode or burn only within a limited concentration range. For example, the concentration limits for methane in air range from 5.3 to
13.9 percent. In the presence of too much air, the fuel becomes too diluted and does not
ignite. On the other hand, if the fuel becomes too concentrated, ignition is prevented
because there is not enough oxygen to support the combustion.
Mixtures at or nearG
the upper concentration limit (“rich” mixtures) explode; however, some gas remainsO
unconsumed because there is not enough oxygen to complete
the combustion. As air rushes back into the origin of the explosion, it combines with the residual
R
hot gas, producing a fire that is characterized
by a whoosh sound. This fire is often more destructive than the explosion that preceded
it.
Mixtures
near the lower end of the limit (“lean” mixtures)
D
generally cause an explosion without accompanying damage due to fire.
O
High explosives
N include dynamite, TNT, PETN, and RDX. They detonate
almost instantaneously at rates of 1,000–8,500 meters per second, producing a smashing or shat, explosives are classified into two groups—primary and
tering effect on their target. High
secondary explosives—based on their sensitivity to heat, shock, or friction.
Primary explosives are ultrasensitive to heat, shock, or friction, and under normal conditions
they detonate violently instead ofJ
burning. For this reason, they are used to detonate other explosives through a chain reaction and
Eare often referred to as primers. Primary explosives provide
the major ingredients of blasting caps and include lead azide, lead styphnate, and diazodinitrophenol
S extreme sensitivity, these explosives are rarely used as the
(see Figure 15–3). Because of their
main charge of a homemade bomb.
S
Secondary explosives are relatively insensitive to heat, shock, or friction, and they normally
I
burn rather than detonate when ignited in small quantities in open air. This group comprises most
C and military blasting. Some common examples of secondhigh explosives used for commercial
ary explosives are dynamite, TNT (trinitrotoluene), PETN (pentaerythritol tetranitrate), RDX
A
(cyclotrimethylenetrinitramine), and tetryl (2,4,6-trinitrophenylmethylnitramine).
HIGH EXPLOSIVES
Dynamite It is an irony of history that the prize most symbolic of humanity’s search for
L bear the name of the developer of one of our most lethal
peace—the Nobel Peace Prize—should
discoveries—dynamite. In 1867,E
the Swedish chemist Alfred Nobel, searching for a method to
desensitize nitroglycerin, found that when kieselguhr, a variety of diatomaceous earth,
I
absorbed a large portion of nitroglycerin,
it became far less sensitive but still retained its
explosive force. Nobel later decided
to
use
pulp
as an absorbent because kieselguhr was a heatG
absorbing material.
H
This so-called pulp dynamite was the beginning of what is now known as the straight dynamite series. These dynamites are used when a quick shattering action is desired. In addition to
nitroglycerine and pulp, present-day
1 straight dynamites also include sodium nitrate (which furnishes oxygen for complete combustion) and a small percentage of a stabilizer, such as calcium
8
carbonate.
All straight dynamite is rated
7 by strength; the strength rating is determined by the weight
percentage of nitroglycerin in the formula. Thus, a 40 percent straight dynamite contains 40 percent
1
nitroglycerin, a 60 percent grade contains
60 percent nitroglycerin, and so forth. However, the relative blasting power of different strengths
of dynamite is not directly proportional to their strength
B
ratings. A 60 percent straight dynamite, rather than being three times as strong as a 20 percent, is
U (see Figure 15–4).
only one and one-half times as strong
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
ISBN 1-256-36593-9
In recent years, nitroglycerin-based dynamite has all but disappeared from the industrial explosives market. Commercially, these explosives have been replaced
mainly by ammonium nitrate–based explosives, that is, water gels, emulsions, and ANFO explosives. These explosives mix oxygen-rich ammonium nitrate with a fuel to form a low-cost, stable
explosive.
Ammonium Nitrate Explosives
FORENSIC INVESTIGATION OF EXPLOSIONS
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FIGURE 15–3
Blasting caps. The left and center caps are initiated by an electrical current;
the right cap is initiated by a safety fuse.
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Typically, water gels have a consistency resembling that of E
set gelatin or gel-type toothpaste.
They are characterized by their water-resistant nature and are employed for all types of blasting
I
under wet conditions. These explosives are based on formulations of ammonium nitrate and
sodium nitrate gelled with a natural polysaccharide such as guarG
gum. Commonly, a combustible
material such as aluminum is mixed into the gel to serve as the explosive’s fuel.
H
Emulsion explosives differ from gels in that they consist of two distinct phases, an oil phase
and a water phase. In these emulsions, a droplet of a supersaturated solution of ammonium nitrate
is surrounded by a hydrocarbon serving as a fuel. A typical emulsion
consists of water, one or
1
more inorganic nitrate oxidizers, oil, and emulsifying agents. Commonly, emulsions contain
8 or microballoons. The size
micron-sized glass, resin, or ceramic spheres known as microspheres
of these spheres controls the explosive’s sensitivity and detonation
7 velocity.
Ammonium nitrate soaked in fuel oil is an explosive known as ANFO. Such commercial explo1
sives are inexpensive and safe to handle and have found wide applications
in blasting operations in
the mining industry. Ammonium nitrate in the form of fertilizer makes
B a readily obtainable ingredient for homemade explosives. Indeed, in an incident related to the 1993 bombing of New York City’s
World Trade Center, the FBI arrested five men during a raid on theirUhideout in New York City, where
they were mixing a “witches’ brew” of fuel oil and an ammonium nitrate–based fertilizer.
Triacetone triperoxide (TATP) is a homemade explosive that has been used as an improvised explosive by terrorist organizations in Israel and other Middle Eastern countries. It is
prepared by reacting the common ingredients of acetone and hydrogen peroxide in the presence
of an acid catalyst such as hydrochloric acid.
TATP
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378
CHAPTER 15
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FIGURE 15–4
S
Sticks of dynamite.
U.S. Department of JusticeAP Wide World
SPhotos
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FIGURE 15–5
A London bus destroyed by a U
TATP-based bomb.
TATP is a friction- and impact-sensitive explosive that is extremely potent when confined in
a container such as a pipe. The 2005 London transit bombings were caused by TATP-based explosives and provide ample evidence that terrorist cells have moved TATP outside the Middle
East. A London bus destroyed by one of the TATP bombs is shown in Figure 15–5.
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
ISBN 1-256-36593-9
Courtesy AP Wide World Photos
FORENSIC INVESTIGATION OF EXPLOSIONS
379
A plot to blow up ten international plane flights leaving Britain for the United States with a
“liquid explosive” apparently involved plans to smuggle the peroxide-based TATP explosive onto
the planes. This plot has prompted authorities to prohibit airline passengers from carrying liquids
and gels onto planes.
No discussion of high explosives would be complete without a mention of military high explosives. In many countries outside the United States, the accessibility
of high explosives to terrorist organizations makes them common constituents of homemade
bombs. RDX, the most popular and powerful military explosive, is often encountered in the
form of a pliable plastic of doughlike consistency known as composition C–4 (a U.S. military
designation).
TNT was produced and used on an enormous scale during World
G War II and may be considered the most important military bursting charge explosive. Alone or in combination with other
O demolition explosives, and
explosives, it has found wide application in shells, bombs, grenades,
propellant compositions (see Figure 15–6). Interestingly, military
R “dynamite” contains no nitroglycerin but is actually composed of a mixture of RDX and TNT. Like other military explosives,
D
TNT is rarely encountered in bombings in the United States.
O projectiles and grenades.
PETN is used by the military in TNT mixtures for small-caliber
Commercially, the chemical is used as the explosive core in a detonating cord or primacord.
N
Instead of the slower-burning safety fuse, a detonating cord is often used to connect a series of
explosive charges so that they will detonate simultaneously. ,
Military High Explosives
Detonators Unlike low explosives, bombs made of high explosives must be detonated by an initiating explosion. In most cases, detonators are blasting caps composed
of copper or aluminum
J
cases filled with lead azide as an initiating charge and PETN or RDX as a detonating charge.
Blasting caps can be initiated by means of a burning safety fuseEor by an electrical current.
Homemade bombs camouflaged in packages, suitcases, and
S the like, are usually initiated
with an electrical blasting cap wired to a battery. An unlimited number of switching-mechanism
S
designs have been devised for setting off these devices; clocks and mercury switches are favored.
Bombers sometimes prefer to employ outside electrical sources.
I For instance, most automobile
bombs are detonated when the ignition switch of a car is turned on.
detonating cord
A cordlike explosive containing a
core of high-explosive material,
usually PETN; also called
primacord
C
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8
7
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FIGURE 15–6
Military explosives in combat use.
Courtesy Getty Images/Time Life Pictures
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CHAPTER 15
forensics at work
Liquid Explosives
In 2006, security agencies in the United States and
Great Britain uncovered a terrorist plot to use liquid
explosives to destroy commercial airlines operating
between the two countries. Of the hundreds of types
of explosives, most are solid. Only about a dozen are
liquid. But some of those liquid explosives can be
readily purchased and others can be made from hundreds of different kinds of chemicals that are not difficult to obtain. After the September 11 attacks,
worries about solid explosives became the primary
concern. In 2001, Richard Reid was arrested for attempting to destroy an American Airlines flight out of
Paris. Authorities later found a high explosive with a
TATP detonator hidden in the lining of his shoe. It is
therefore not surprising that terrorists turned to liquids in this latest plot. A memo issued by federal security officials about the plot to blow up ten
international planes highlighted a type of liquid explosive based on peroxide.
Gels discarded by airline passengers before boarding.
Stefano Paltera, AP Wide World Photos
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Collection and Analysis
H
of Evidence of Explosives
The most important step in the detection and analysis of explosive residues is the collection of
appropriate samples from the explosion
1 scene. Invariably, undetonated residues of the explosive
remain at the site of the explosion. The detection and identification of these explosives in the lab8
oratory depends on the bomb-scene investigator’s skill and ability to recognize and sample the
areas most likely to contain such 7
materials.
1
Detecting and Recovering
B Evidence of Explosives
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
ISBN 1-256-36593-9
The most obvious characteristic of a high or contained low explosive is the presence of a crater at
the origin of the blast. Once theU
crater has been located, all loose soil and other debris must
immediately be removed from the interior of the hole and preserved for laboratory analysis. Other
good sources of explosive residues are objects located near the origin of detonation. Wood, insulation, rubber, and other soft materials that are readily penetrated often collect traces of the explosive.
However, nonporous objects near the blast must not be overlooked. For instance, residues can be
FORENSIC INVESTIGATION OF EXPLOSIONS
381
forensics at work
The most common peroxide-based explosive is
TATP (triacetone triperoxide), which is made up of
acetone and hydrogen peroxide, two widely available
substances. TATP can be used as a detonator or a primary explosive and has been used in Qaeda-related
bomb plots and by Palestinian suicide bombers. TATP
itself is a white powder made up of crystals that
form when acetone and hydrogen peroxide are mixed
together, usually with a catalyst added to speed the
chemical reactions. Acetone is the main ingredient in
nail polish remover, while hydrogen peroxide is a popular antiseptic. When the two main ingredients are
mixed, they form a white powder that can be easily detonated using an electrical spark.
Commercially available hydrogen peroxide, however,
is not concentrated enough to create TATP. The solution
sold in stores contains about 3 percent hydrogen peroxide, compared to the approximately 70 percent concentration need for TATP. However, hydrogen peroxide
solutions of up to 30 percent can be obtained from
chemical supply houses. According to explosives experts,
a mixture of 30 percent hydrogen peroxide and acetone
can create a fire hot enough to burn though the fuselage
of an aircraft.
In theory, scientists know how to detect peroxidebased
explosives. The challenge is to design machines
G
that can perform scans quickly and efficiently on thouO sands of passengers passing through airport security
R checks. Current scanning machines at airports are
to detect nitrogen containing chemicals and
D designed
are not designed to detect peroxide-containing exploO sive ingredients. Since 9/11, security experts have
N worried about the possibility of liquid explosives in the
form of liquids and gels getting onto airliners.
,
Without the luxury of waiting for newly designed
scanning devices capable of ferreting out dangerous
liquids to be in place at airports, the decision was made
J to use a common-sense approach—that is, to restrict
E the types and quantities of liquids that a passenger can
carry onto a plane.
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found on the surfaces of metal objects near the site of an explosion.
G Material blown away from the
blast’s origin should also be recovered because it, too, may retain explosive residues.
H
The entire area must be systematically searched, with great care given to recovering any trace
of a detonating mechanism or any other item foreign to the explosion site. Wire-mesh screens are
best used for sifting through debris. All personnel involved in searching the bomb scene must
1
take appropriate measures to avoid contaminating the scene, including dressing in disposable
8
gloves, shoe covers, and overalls.
ISBN 1-256-36593-9
7 of the explosive are frequently
ION MOBILITY SPECTROMETER In pipe-bomb explosions, particles
found adhering to the pipe cap or to the pipe threads, as a result of either
1 being impacted into the metal
by the force of the explosion or being deposited in the threads during the construction of the bomb.
One approach for screening objects for the presence of explosive B
residues in the field or the laboratory is the ion mobility spectrometer (IMS).1 A portable IMS is shown
U in Figure 15–7.
1
T. Keller et al., “Application of Ion Mobility Spectrometry in Cases of Forensic Interest,” Forensic Science
International 161 (2006): 130.
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
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CHAPTER 15
FIGURE 15–7
A portable ion mobility
spectrometer used to rapidly
detect and tentatively identify
trace quantities of explosives.
Courtesy GE Ion Track, Wilmington,
Mass. 01887
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This handheld detector uses S
a vacuum to collect explosive residues from suspect surfaces.
Alternatively, the surface suspected
Sof containing explosive residues is wiped down with a Tefloncoated fiberglass disc and the collected residues are then drawn into the spectrometer off the disc.
I
Once in the IMS, the explosive residues
are vaporized by the application of heat. These vaporized substances are exposed to a beam
of
electrons
or beta rays emitted by radioactive nickel and
C
converted into electrically charged molecules or ions. The ions are then allowed to move through a
A of an electric field. A schematic diagram of an IMS is
tube (drift region) under the influence
shown in Figure 15–8.
The preliminary identification of an explosive residue can be made by noting the time it takes
the explosive to move through theL
tube. Because ions move at different speeds depending on their
size and structure, they can be characterized
by the speed at which they pass through the tube.
E
Used as a screening tool, this method rapidly detects a full range of explosives, even at low
I
detection levels. However, all results need to be verified through confirmatory tests.
The IMS can detect plastic explosives
as well as commercial and military explosives. More
G
than 10,000 portable and full-size IMS units are currently used at airport security checkpoints,
H
and more than 50,000 handheld IMS analyzers have been deployed for chemical-weapons
monitoring in various armed forces.
1All materials collected for examination by the laboratory must
be placed in airtight sealed containers
8 and labeled with all pertinent information. Soil and other
soft loose materials are best stored in metal airtight containers such as clean paint cans. Debris
7 areas are to be packaged in separate airtight containers. Plasand articles collected from different
tic bags should not be used to store
1 evidence suspected of containing explosive residues. Some
explosives can actually escape through the plastic. Sharp-edged objects should not be allowed to
pierce the sides of a plastic bag. ItBis best to place these types of items in metal containers.
COLLECTION AND PACKAGING
U
When the bomb-scene debris and other materials arrive at the laboratory, everything is first
examined microscopically to detect particles of unconsumed explosive. Portions of the recovered
debris and detonating mechanism, if found, are carefully viewed under a low-power stereoscopic
microscope in a painstaking effort to locate particles of the explosive. Black powder and smokeless powder are relatively easy to locate in debris because of their characteristic shapes and colors
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ISBN 1-256-36593-9
Analysis of Evidence of Explosives
FORENSIC INVESTIGATION OF EXPLOSIONS
Sample is
drawn into
ionization
chamber
Sample is bombarded
by radioactive particles
emitted by an isotope
of nickel to form ions
Drift rings
63
Ni
Collection
electrode
Shutter
Ionization chamber
(a)
Sample is converted into ions
of different sizes and structures
G
O
Drift region
R
D
O
Drift rings
N
,
Shutter
Ionization chamber
Drift region
(b)
Drift rings
Collection
J
electrode
E
S
S
I
C
AExplosive substances can
be characterized by the
speed at which they move
through the electric field
L
E
I
G
H
Collection
electrode
Shutter
ISBN 1-256-36593-9
1
Ionization chamber
Drift region 8 Ions separate as they move
7 through an electric field
(c)
1
FIGURE 15–8
Schematic diagram of an ion mobility spectrometer. A sample
B is introduced into
an ionization chamber, where bombardment with radioactive particles emitted
U
by an isotope of nickel converts the sample to ions. The ions move into a drift
region where ion separation occurs based on the speed of the ions as they
move through an electric field.
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383
384
CHAPTER 15
TABLE 15–1
Color Spot Tests for Common Explosives
Reagent
a
Substance
Greiss
Chlorate
Nitrate
Nitrocellulose
Nitroglycerin
PETN
RDX
TNT
Tetryl
No color
Pink to red
Pink
Pink to red
Pink to red
G
Pink to red
No colorO
Pink to red
a
R
D
O
N
,
Diphenylamineb
Alcoholic KOHc
Blue
Blue
Blue-black
Blue
Blue
Blue
No color
Blue
No color
No color
No color
No color
No color
No color
Red
Red-violet
Greiss reagent: Solution 1—Dissolve 1 g sulfanilic acid in 100 mL 30% acetic acid. Solution 2—Dissolve 0.5 g
N-(1-napthyl) ethylenediamine in 100 mL methyl alcohol. Add solutions 1 and 2 and a few milligrams of zinc
dust to the suspect extract.
b
Diphenylamine reagent: Dissolve 1 g diphenylamine in 100 mL concentrated sulfuric acid.
c
Alcoholic KOH reagent: Dissolve 10 g of potassium hydroxide in 100 mL absolute alcohol.
(see Figure 15–2). However, dynamite and other high explosives present the microscopist with a
J
much more difficult task and often must be detected by other means.
E the recovered debris is thoroughly rinsed with acetone. The
Following microscopic examination,
high solubility of most explosives in acetone ensures their quick removal from the debris. When a
S
water-gel explosive containing ammonium nitrate or a low explosive is suspected, the debris should
S substances (such as nitrates and chlorates) will be extracted.
be rinsed with water so that water-soluble
Table 15–1 lists a number of simple
I color tests the examiner can perform on the acetone and water
extracts to screen for the presence of organic and inorganic explosives, respectively.
C
Once collected, the acetone extract is concentrated
A thin-layer chromatography (TLC), high-performance liquid
and analyzed using color spot tests,
SCREENING AND CONFIRMATION TESTS
chromatography (HPLC; see pages 127–128), and gas chromatography/mass spectrometry. The
presence of an explosive is indicated by a well-defined spot on a TLC plate with an Rf value
L
corresponding to a known explosive—for
example, nitroglycerin, RDX, or PETN.
The high sensitivity of HPLCE
also makes it useful for analyzing trace evidence of explosives.
HPLC operates at room temperature and hence does not cause explosives, many of which are temI
perature sensitive, to decompose during their analysis. When a water-gel explosive containing
G is suspected, the debris should be rinsed with water so that
ammonium nitrate or a low explosive
water-soluble substances (such asH
nitrates and chlorates) will be extracted.
When sufficient quantities of explosives are recoverable, confirmatory tests may be
performed by either infrared spectrophotometry or X-ray diffraction. The former produces a
unique “fingerprint” pattern for an
1 organic explosive, as shown by the IR spectrum of RDX in
Figure 15–9. The latter provides a unique diffraction pattern for inorganic substances such as
8
potassium nitrate and potassium chlorate,
shown in Figure 6–11.
7 program has been proposed to further enhance a bombAn explosive “taggant”
scene investigator’s chances of recovering
useful evidence at a postexplosion scene. Under this
1
proposal, tiny color-coded chips the size of sand grains would be added to commercial explosives
B
during their manufacture. Some of these chips would be expected to survive an explosion and be
capable of recovery at explosion U
scenes. To aid in their recovery, the chips are made both fluorescent and magnetic sensitive. Hence, investigators can search for taggants at the explosion site
with magnetic tools and ultraviolet light.
The taggant chip is arranged in a color sequence that indicates where the explosive was made
and when it was produced (see Figure 15–10). With this knowledge, the explosive can be traced
through its distribution chain to its final legal possessor. The taggant colors are readily observed
and are read with the aid of a low-power microscope.
TAGGANTS
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FORENSIC INVESTIGATION OF EXPLOSIONS
385
Wavelength μm
3
4
5
6
7
8
9
10
100
12 13 14 15 16
100
90
90
80
80
70
70
60
60
50
40
30
Transmittance
11
20
10
0
3800 3500
3000
Wavenumber cm–1
2500
FIGURE 15–9
Infrared spectrum of RDX.
Fluorescent
spotter
2000
1800
G
O
R
D
O
N
,
1600
50
40
30
20
10
1400
1200
1000
800
0
625
J
E
S
S
I
C
A
L
E
FIGURE 15–10
I
Cross-section of a taggant. The color sequence of the recovered
taggant is observed
with the aid of a low-power microscope. The colors are then
matched
to a color code
G
to yield information about the plant of manufacture, production lot, and purchasers of
H
the explosive material.
1 2 3 4 5 6 7 8
1
There are no plans to institute a taggant program for commercial
explosives in the United
States. In Europe, only Switzerland has adopted a taggant program;
8 thus, it is extremely doubtful
that taggants will be found in any significant number of bombing incidents in the foreseeable
7
future. Interestingly, the International Civil Aviation Organization has mandated that a volatile
taggant be added to plastic explosives during their manufacture 1
in order to facilitate the detection
of these explosives. Programs are now under way to tag commercial C–4 with the volatile
B
chemical known as DMNB (2,3-dimethyl-2,3-dinitrobutane).
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U
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386
CHAPTER 15
chapter summary
>>>>>>>>>>>
Explosives are substances that undergo a rapid oxidation
reaction with the production of large quantities of gases. This
sudden buildup of gas pressure constitutes an explosion. The
speed at which explosives decompose permits their classification as high or low explosives.
The most widely used low explosives are black powder
and smokeless powder. Among the high explosives, primary
explosives are ultrasensitive to heat, shock, or friction and
provide the major ingredients found in blasting caps. Secondary explosives normally constitute the main charge of a
high explosive.
Among the high explosives, nitroglycerin-based dynamite
has all but disappeared from the industrial explosives market
and has been replaced by ammonium nitrate–based explosives
(such as water gels, emulsions, and ANFO explosives). In
many countries outside the United States, the accessibility of
review questions
1. Oxidizing agents supply ___________ to a chemical
reaction.
2. Three ingredients of black powder are ___________,
___________, and ___________.
3. Rapid combustion accompanied by the creation of large
volumes of gases describes a(n) ___________.
4. Explosives that decompose at relatively slow rates are
classified as ___________ explosives.
5. ___________ explosives detonate almost instantaneously to produce a smashing or shattering effect.
6. The most widely used low explosives are ___________
and ___________.
7. A low explosive becomes explosive and lethal only when
it is ___________.
8. True or False: Air and a gaseous fuel burn when mixed
at any concentration range. ___________
S
S
I
C
12.
A
The most widely used explosive in the military is
___________.
13. The explosive core in detonating cord is ___________.
L14. A high explosive is normally detonated by a(n)
___________ explosive contained within a blasting cap.
E
15.
I
G16.
H
17.
1
8
18.
7
1
B19.
U
20.
21.
An obvious characteristic of a high explosive is the presence of a(n) ___________ at the origin of the blast.
The most important step in detecting explosive residues
is the ___________ of appropriate samples from the
explosion scene.
To screen objects for the presence of explosive residues
in the field or the laboratory, the investigator may use a
handheld ___________.
Unconsumed explosive residues may be detected in the
laboratory through a careful ___________ examination
of the debris.
Debris recovered from the site of an explosion is routinely rinsed with ___________ in an attempt to recover
high-explosive residues.
Once collected, the acetone extract is initially analyzed
by ___________, ___________, and ___________.
The technique of ___________ produces a unique
absorption spectrum for an organic explosive.
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ISBN 1-256-36593-9
9. High explosives can be classified as either ___________
or ___________ explosives.
10. The blasting power of different dynamite strengths (is, is
not) in direct proportion to the weight percentage of
nitroglycerin.
11. True or False: The most common commercial explosives
incorporate ammonium nitrate. ___________
military high explosives to terrorist organizations makes them
Gcommon constituents of homemade bombs. RDX is the most
popular and powerful of the military explosives.
O The entire bomb site must be systematically searched
Rwith great care given to recovering any trace of a detonating
or any other item foreign to the explosion site.
Dmechanism
Objects located at or near the origin of the explosion must be
Ocollected for laboratory examination.
N Typically, in the laboratory, debris collected at explosion
scenes is examined microscopically for unconsumed explosive
, particles. Recovered debris may also be thoroughly rinsed
with organic solvents and analyzed by testing procedures that
include color spot tests, thin-layer chromatography, highJperformance liquid chromatography, and gas chromatography/
Emass spectrometry.
FORENSIC INVESTIGATION OF EXPLOSIONS
22. The technique of ___________ provides a unique diffraction pattern for the identification of the inorganic
constituents of explosives.
23. True or False: Debris and articles at an explosion scene
that are collected from different areas are to be packaged
in separate airtight containers.___________
387
24. True or False: In the absence of airtight metal containers,
plastic bags can be used to store evidence suspected of
containing explosive residues.___________
application and critical thinking
1. The following pieces of evidence were found at separate
explosion sites. For each item, indicate whether the explosion was more likely caused by low or high explosives, and explain your answer:
a. Lead azide residues
b. Nitrocellulose residues
c. Ammonium nitrate residues
d. Scraps of primacord
e. Potassium chlorate residues
2. Which color test or tests would you run first on a suspect
sample to test for evidence of each of the following
explosives? Explain your answers.
a. Tetryl
b. TNT
c. Chlorate
d. Nitrocellulose
further references
Thurman, J. T., Practical Bomb Scene Investigation. Boca
Raton, Fla.: Taylor & Francis, 2006.
G
O
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D
O
N
,
J
E
S
S
I
C
A
3. Criminalist Matt Weir is collecting evidence from the
site of an explosion. Arriving on the scene, he immediately proceeds to look for the crater caused by the blast.
After finding the crater, he picks through the debris at the
site by hand, looking for evidence of detonators or foreign materials. Matt collects loose soil and debris from
the immediate area, placing the smaller bits in paper
folded into a druggist fold. Larger items he stores in plastic bags for transportation to the laboratory. What mistakes, if any, did Matt make in collecting and storing this
evidence?
L
E
I Yinon, J., Forensic and Environmental Detection of Explosives. West Sussex, England: Wiley, 1999.
G
H
ISBN 1-256-36593-9
1
8
7
1
B
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headline news
James Earl Ray: Conspirator or Lone Gunman?
Since his arrest in 1968 for the assassination
G
of Dr. Martin
Luther King, Jr., endless speculation
has swirledOaround the motives and connections of James
R was a career criminal who was serving time for
Earl Ray. Ray
armed robbery
when he escaped from the Missouri State
D
Prison almost
O one year before the assassination. On April 3,
1968, Ray
N arrived in Memphis, Tennessee. The next day
he rented a room at Bessie Brewer’s Rooming House,
,
across the street from the Lorraine Motel where Dr. King
was staying.
J
At 6:00 p.m., Dr. King left his second-story motel
E
room and stepped onto the balcony of the Lorraine
S As King turned toward his room, a shot rang
Motel.
S striking the civil rights activist. Nothing could be
out,
Idone to revive him, and Dr. King was pronounced
Cdead at 7:05 p.m. As the assailant ran on foot from
A Bessie Brewer’s, he left a blanket-covered
package in front of a nearby building and then
L drove off in a white Mustang. The package was
E later shown to contain a high-powered rifle
equipped with a scope, a radio, some clothes,
I
a pair of binoculars, a couple of beer cans, and a receipt
G
for the binoculars. Almost a week after the shooting, the white
H
Mustang was found abandoned in Atlanta, Georgia.
Fingerprints later identified as James Earl Ray’s were found in the Mustang, on the rifle,
1 a guilty plea in return for a sentence of ninetyon the binoculars, and on a beer can. In 1969, Ray entered
8
nine years. Although a variety of conspiracy theories surround
this crime, the indisputable fact is that a
fingerprint put the rifle that killed Martin Luther King, Jr.,
7 in the hands of James Earl Ray.
1
B
U
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>>>>>>>>>>>>
chapter
16
fingerprints
J
E
S
After studying this chapter you should
be able to:
Sa fingerprint
• Know the common ridge characteristics of
I
• List the three major fingerprint patterns and their respective
C
subclasses
A
• Distinguish visible, plastic, and latent fingerprints
• Describe the concept of an automated fingerprint
L
identification system (AFIS)
E
• List the techniques for developing latent fingerprints on
I
porous and nonporous objects
G
• Describe the proper procedures for preserving
a developed
latent fingerprint
H
1
8
7
1
B
U
KEY TERMS
anthropometry
arch
digital imaging
fluoresce
iodine fuming
latent fingerprint
livescan
loop
ninhydrin
Physical Developer
pixel
plastic print
portrait parlé
ridge characteristics
(minutiae)
sublimation
superglue fuming
visible print
whorl
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Learning Objectives
G
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390
CHAPTER 16
History of Fingerprinting
portrait parlé
A verbal description of a
perpetrator’s physical
characteristics and dress provided
by an eyewitness
anthropometry
A system of identification of
individuals by measurement of
parts of the body, developed by
Alphonse Bertillon
Since the beginnings of criminal investigation, police have sought an infallible means of human
identification. The first systematic attempt at personal identification was devised and introduced
by a French police expert, Alphonse Bertillon, in 1883. The Bertillon system relied on a detailed
description (portrait parlé) of the subject, combined with full-length and profile photographs and
a system of precise body measurements known as anthropometry.
The use of anthropometry as a method of identification rested on the premise that the dimensions of the human bone system remained fixed from age 20 until death. Skeleton sizes were
thought to be so extremely diverse that no two individuals could have exactly the same measurements. Bertillon recommended routine taking of eleven measurements of the human anatomy.
G of head, and length of the left foot (see Figure 1–2).
These included height, reach, width
For two decades, this system O
was considered the most accurate method of identification. But
in the first years of the new century, police began to appreciate and accept a system of identification based on the classification ofR
finger ridge patterns known as fingerprints. Today, the fingerprint is the pillar of modern criminal
D identification.
O
N the fingerprint to sign legal documents as far back as three
Evidence exists that the Chinese used
thousand years ago. However, whether
this practice was performed for ceremonial custom or as
,
Early Use of Fingerprints
a means of personal identity remains a point of conjecture lost to history. In any case, the examples of fingerprinting in ancient history are ambiguous, and the few that exist did not contribute
J techniques as we know them today.
to the development of fingerprinting
Several years before Bertillon began work on his system, William Herschel, an English civil
E
servant stationed in India, started the practice of requiring Indian citizens to sign contracts with the imS pressed against a stamp pad for the purpose. The motives for
print of their right hand, which was
Herschel’s requirement remain unclear;
S he may have envisioned fingerprinting as a means of personal identification or just as a form of the Hindu custom that a trace of bodily contact was more
I In any case, he did not publish anything about his activibinding than a signature on a contract.
ties until after a Scottish physician,
C Henry Fauld, working in a hospital in Japan, published his
views on the potential application of fingerprinting to personal identification.
In 1880, Fauld suggested thatAskin ridge patterns could be important for the identification of
criminals. He told about a thief who left his fingerprint on a whitewashed wall, and how in comparing these prints with those of a suspect, he found that they were quite different. A few days
L fingerprints compared with those on the wall. When conlater another suspect was found whose
fronted with this evidence, the individual
confessed to the crime.
E
Fauld was convinced that fingerprints furnished infallible proof of identification. He even ofI
fered to set up, at his own expense, a fingerprint bureau at Scotland Yard to test the practicality of
G in favor of the Bertillon system. This decision was reversed
the method. But his offer was rejected
less than two decades later.
H
Early Classification of Fingerprints
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1
The extensive research into fingerprinting
conducted by another Englishman, Francis Galton,
provided the needed impetus that made
police
agencies aware of its potential application. In 1892,
8
Galton published his classic textbook Finger Prints, the first book of its kind on the subject. In
7 of fingerprints and suggested methods for recording them.
his book, he discussed the anatomy
Galton also proposed assigning fingerprints
to three pattern types—loops, arches, and whorls.
1
Most important, the book demonstrated that no two prints were identical and that an individual’s
prints remained unchanged fromByear to year. At Galton’s insistence, the British government
adopted fingerprinting as a supplement
U to the Bertillon system.
The next step in the development of fingerprint technology was the creation of classification
systems capable of filing thousands of prints in a logical and searchable sequence. Dr. Juan
Vucetich, an Argentinian police officer fascinated by Galton’s work, devised a workable concept
in 1891. His classification system has been refined over the years and is still widely used today in
most Spanish-speaking countries. In 1897, another classification system was proposed by an
Englishman, Sir Edward Richard Henry. Four years later, Henry’s system was adopted by Scotland
FINGERPRINTS
391
Yard. Today, most English-speaking countries, including the United States, use some version of
Henry’s classification system to file fingerprints.
Adoption of Fingerprinting
Early in the 20th century, Bertillon’s measurement system began to fall into disfavor. Its results
were highly susceptible to error, particularly when the measurements were taken by people who
were not thoroughly trained. The method was dealt its most severe and notable setback in 1903
when a convict, Will West, arrived at Fort Leavenworth prison. A routine check of the prison files
startlingly revealed that a William West, already in the prison, could not be distinguished from the
new prisoner by body measurements or even by photographs. In fact, the two men looked just like
twins, and their measurements were practically the same. Subsequently, fingerprints of the prisG
oners clearly distinguished them.
In the United States, the first systematic and official use of O
fingerprints for personal identification was adopted by the New York City Civil Service Commission in 1901. The method was
R
used for certifying all civil service applications. Several American police officials received instruction in fingerprint identification at the 1904 World’s Fair in D
St. Louis from representatives of
Scotland Yard. After the fair and the Will West incident, fingerprinting began to be used in earnest
O
in all major cities of the United States. In 1924, the fingerprint records of the Bureau of Investigation and Leavenworth were merged to form the nucleus of theN
identification records of the new
Federal Bureau of Investigation. The FBI has the largest collection
, of fingerprints in the world.
By the beginning of World War I, England and practically all of Europe had adopted fingerprinting as their primary method of identifying criminals.
In 1999, the admissibility of fingerprint evidence was challenged
J in the case of United States v.
Byron C. Mitchell in the Eastern District of Pennsylvania. The defendant’s attorneys argued that
E in Daubert (see pages 16–17).
fingerprints could not be proven unique under the guidelines cited
Government experts vigorously disputed this claim. After a four-and-a-half-day
Daubert hearing,
S
the judge upheld the admissibility of fingerprints as scientific evidence and ruled that (1) human
S ridge skin arrangements are
friction ridges are unique and permanent and (2) human friction
unique and permanent.
I
Fundamental Principles of
C
A
Fingerprints
First Principle: A Fingerprint Is an Individual Characteristic;
L
No Two Fingers Have Yet Been Found to Possess
Identical
Ridge Characteristics
E
The acceptance of fingerprint evidence by the courts has always been predicated on the assumpI
tion that no two individuals have identical fingerprints. Early fingerprint experts consistently referred to Galton’s calculation, showing the possible existence ofG
64 billion different fingerprints,
to support this contention. Later, researchers questioned the H
validity of Galton’s figures and
attempted to devise mathematical models to better approximate this value. However, no matter
what mathematical model one refers to, the conclusions are always the same: the probability for
the existence of two identical fingerprint patterns in the world’s1population is extremely small.
Not only is this principle supported by theoretical calculations, but just as important, it is ver8 during the past 110 years—
ified by the millions of individuals who have had their prints classified
no two have ever been found to be identical. The FBI has nearly750 million fingerprint records in
its computer database and has yet to find an identical image belonging to two different people.
1
The individuality of a fingerprint is not determined by its general
B
shape or pattern but by a careful study of its ridge characteristics (also known as minutiae). The
identity, number, and relative location of characteristics such asUthose illustrated in Figure 16–1
impart individuality to a fingerprint. If two prints are to match, they must reveal characteristics
that not only are identical but have the same relative location to one another in a print. In a judicial proceeding, a point-by-point comparison must be demonstrated by the expert, using charts
similar to the one shown in Figure 16–2, in order to prove the identity of an individual.
If an expert were asked to compare the characteristics of the complete fingerprint, no difficulty would be encountered in completing such an assignment; the average fingerprint has as
ISBN 1-256-36593-9
RIDGE CHARACTERISTICS
ridge characteristics
(minutiae)
Ridge endings, bifurcations,
enclosures, and other ridge details,
which must match in two
fingerprints in order for their
common origin to be established
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392
CHAPTER 16
Bifurcation
Ridge Ending
Ridge
Endings
Enclosure
G
O
R
D
FIGURE 16–1
O
Fingerprint ridge characteristics.
Courtesy Sirchie Fingerprint Laboratories,N
Youngsville, N.C., www.sirchie.com
,
Ridge Island
(Ridge Dot)
Bifurcation
J
E
S
S
I
C
A
L
E
I
G
H
FIGURE 16–2
A fingerprint exhibit illustrating1the matching ridge characteristics between the crimeof one of the suspect’s fingers.
scene print and an inked impression
8
7
many as 150 individual ridge characteristics.
However, most prints recovered at crime scenes are
partial impressions, showing only1a segment of the entire print. Under these circumstances, the
expert can compare only a small number of ridge characteristics from the recovered print to a
B
known recorded print.
U
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
ISBN 1-256-36593-9
For years, experts have debated how many ridge comparisons are necessary to identify two fingerprints as the same. Numbers that range from 8 to 16 have been suggested as being sufficient to meet the criteria of individuality. However, the difficulty in
establishing such a minimum is that no comprehensive statistical study has ever been undertaken
to determine the frequency of occurrence of different ridge characteristics and their relative
locations. Until such a study is undertaken and completed, no meaningful guidelines can be
established for defining the uniqueness of a fingerprint.
RIDGE COMPARISONS
FINGERPRINTS
393
In 1973, the International Association for Identification, after a three-year study of this question, concluded that “no valid basis exists for requiring a predetermined minimum number of friction ridge characteristics which must be present in two impressions in order to establish positive
identification.” Hence, the final determination must be based on the experience and knowledge
of the expert, with the understanding that others may profess honest differences of opinion on the
uniqueness of a fingerprint if the question of minimal number of ridge characteristics exists. In
1995, members of the international fingerprint community at a conference in Israel issued the
Ne’urim Declaration, which supported the 1973 International Association for Identification
resolution.
Second Principle: A Fingerprint Remains Unchanged
G
During an Individual’s Lifetime
Fingerprints are a reproduction of friction skin ridges found onO
the palm side of the fingers and
thumbs. Similar friction skin can also be found on the surface of the palms and soles of the feet.
R
Apparently, these skin surfaces have been designed by nature to provide our bodies with a firmer
grasp and a resistance to slippage. A visual inspection of frictionD
skin reveals a series of lines corresponding to hills (ridges) and valleys (grooves). The shape andO
form of the skin ridges are what
one sees as the black lines of an inked fingerprint impression.
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Skin is composed of layers of cells. Those nearest the surface make
, skin is known as the dermis.
up the outer portion of the skin known as the epidermis, and the inner
A cross section of skin (see Figure 16–3) reveals a boundary of cells separating the epidermis and
dermis. The shape of this boundary, made up of dermal papillae, determines the form and pattern
J
of the ridges on the surface of the skin. Once the dermal papillae develop in the human fetus, the
ridge patterns remain unchanged throughout life except to enlarge
E during growth.
Each skin ridge is populated by a single row of pores that are the openings for ducts leading
S
from the sweat glands. Through these pores, perspiration is discharged and deposited on the surS along with oils that may have
face of the skin. Once the finger touches a surface, perspiration,
been picked up by touching the hairy portions of the body, is transferred
onto that surface, thereby
I
leaving an impression of the finger’s ridge pattern (a fingerprint). Prints deposited in this manner
C
are invisible to the eye and are commonly referred to as latent fingerprints.
latent fingerprint
A one’s fingerprints, there has
Although it is impossible to change
been no lack of effort on the part of some criminals to obscure them. If an injury reaches deeply
A fingerprint made by the deposit
of oils and/or perspiration; it is
invisible to the naked eye
STRUCTURE OF THE SKIN
CHANGING FINGERPRINTS
Ridge island
Sweat pores
Epidermis
Papillae
Dermis
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Duct of sweat gland
Sweat gland
Nerves of touch
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FIGURE 16–3
Cross-section of human skin.
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FIGURE 16–4
D
The right index finger impression
O of John Dillinger, before scarification on the left and
afterward on the right. Comparison is proved by the 14 matching ridge characteristics.
N
Courtesy Institute of Applied Science, Youngsville,
N.C.
,
enough into the skin and damages the dermal papillae, a permanent scar will form. However, for
this to happen, such a wound would have to penetrate 1 to 2 millimeters beneath the skin’s surJ scarring the skin can only be self-defeating, for it would be
face. Indeed, efforts at intentionally
totally impossible to obliterate allEof the ridge characteristics on the hand, and the presence of
permanent scars merely provides new characteristics for identification.
Perhaps the most publicized S
attempt at obliteration was that of the notorious gangster John
Dillinger, who tried to destroy hisSown fingerprints by applying a corrosive acid to them. Prints
taken at the morgue after he was shot to death, compared with fingerprints recorded at the time
I efforts had been fruitless (see Figure 16–4).
of a previous arrest, proved that his
C
Third Principle: Fingerprints
Have General Ridge Patterns
A
That Permit Them to Be Systematically Classified
All fingerprints are divided into three classes on the basis of their general pattern: loops, whorls,
and arches. Sixty to 65 percent ofLthe population have loops, 30 to 35 percent have whorls, and
about 5 percent have arches. These
E three classes form the basis for all ten-finger classification
systems presently in use.
I
loop
A typical loop pattern is illustrated in Figure 16–5. A loop must have one or more
G
ridges entering from one side of the print, recurving, and exiting from the same side. If the loop
opens toward the little finger, it isH
called an ulnar loop; if it opens toward the thumb, it is a radial
loop. The pattern area of the loop is surrounded by two diverging ridges known as type lines. The
ridge point at or nearest the type-line divergence and located at or directly in front of the point
1 To many, a fingerprint delta resembles the silt formation that
of divergence is known as the delta.
builds up as a river flows into the8entrance of a lake—hence, the analogy to the geological formation known as a delta. All loops must have one delta. The core, as the name suggests, is the
approximate center of the pattern.7
LOOPS
A class of fingerprints characterized
by ridge lines that enter from one
side of the pattern and curve
around to exit from the same side
of the pattern
arch
1 into four distinct groups, as shown in Figure 16–6: plain,
Whorls are actually divided
central pocket loop, double loop, and
B accidental. All whorl patterns must have type lines and at least
two deltas. A plain whorl and a central pocket loop have at least one ridge that makes a complete
U of a spiral, oval, or any variant of a circle. If an imaginary line
circuit. This ridge may be in the form
drawn between the two deltas contained within these two patterns touches any one of the spiral
ridges, the pattern is a plain whorl. If no such ridge is touched, the pattern is a central pocket loop.
A class of fingerprints characterized
by ridge lines that enter the print
from one side and flow out the
other side
ARCHES Arches, the least common of the three general patterns, are subdivided into two distinct groups: plain arches and tented arches, as shown in Figure 16–7. The plain arch is the simplest of all fingerprint patterns; it is formed by ridges entering from one side of the print and
whorl
A class of fingerprints that includes
ridge patterns that are generally
rounded or circular in shape and
have two deltas
WHORLS
ISBN 1-256-36593-9
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
FINGERPRINTS
FIGURE 16–5
Loop pattern.
Core
Type line
Delta
Type line
Plain whorl
Central pocket
loop
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Double loop
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FIGURE 16–6
Whorl patterns.
Accidental
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Plain
FIGURE 16–7
Arch patterns.
Tented
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exiting on the opposite side. Generally, these ridges tend to rise in the center of the pattern, formE except that instead of rising
ing a wavelike pattern. The tented arch is similar to the plain arch
smoothly at the center, there is a sharp upthrust or spike, or the ridges
I meet at an angle that is less
than 90 degrees.1 Arches do not have type lines, deltas, or cores.
G
As the name implies, the double loop is made up of two loops combined into
H two or more patterns (not
one fingerprint. Any whorl classified as an accidental either contains
including the plain arch) or is a pattern not covered by other categories. Hence, an accidental may
consist of a combination loop and plain whorl or loop and tented arch.
1
With a knowledge of basic fingerprint pattern classes, we can now begin to develop an appreciation for fingerprint classification systems. However, the subject
is far more complex than
8
can be described in a textbook of this nature. The student seeking a more detailed treatment of the
7
subject would do well to consult the references cited at the end of the chapter.
OTHER PATTERNS
ISBN 1-256-36593-9
Classification of
1
Fingerprints B
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The original Henry system, as it was adopted by Scotland Yard in 1901, converted ridge patterns
on all ten fingers into a series of letters and numbers arranged in the form of a fraction. However,
the system as it was originally designed could accommodate files of up to only 100,000 sets of
1
A tented arch is also any pattern that resembles a loop but lacks one of the essential requirements for classification as
a loop.
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prints; thus, as collections grew in size, it became necessary to expand the capacity of the classification system. In the United States, the FBI, faced with the problem of filing ever-increasing
numbers of prints, expanded its classification capacity by modifying and extending the original
Henry system. These modifications are collectively known as the FBI system and are used by
most agencies in the United States today.
The Primary Classification
Although we will not discuss all of the different divisions of the FBI system, a description of just
one part, the primary classification, will provide an interesting insight into the process of fingerprint classification.
The primary classification is part of the original Henry system and provides the first classiG this classification alone, all of the fingerprint cards in the
fication step in the FBI system. Using
world could be divided into 1,024O
groups. The first step in obtaining the primary classification is
to pair up fingers, placing one finger in the numerator of a fraction, the other in the denominator.
R
The fingers are paired in the following sequence:
D
L. Thumb L. Middle L. Little
O
R. Thumb R. Middle
R. Little
L. Index
L. Ring
N
The presence or absence of the whorl pattern is the basis for determination of the primary
classification. If a whorl pattern is,found on any finger of the first pair, it is assigned a value of 16;
R. Index
R. Ring
on the second pair, a value of 8; on the third pair, a value of 4; on the fourth pair, a value of 2; and
on the last pair, a value of 1. Any finger with an arch or loop pattern is assigned a value of 0.
After values for all ten fingers
Jare obtained in this manner, they are totaled, and 1 is added to
both the numerator and denominator. The fraction thus obtained is the primary classification. For
E
example, if the right index and right middle fingers are whorls and all the others are loops, the
S
primary classification is
S16 ⫹ 0 ⫹ 0 ⫹ 0 ⫹ 0 ⫹ 1
17
⫽
9
I 0⫹8⫹0⫹0⫹0⫹1
Approximately 25 percent ofC
the population falls into the 1/1 category; that is, all their fingers
have either loops or arches.
A
A fingerprint classification system cannot in itself unequivocally identify an individual; it
merely provides the fingerprint examiner with a number of candidates, all of whom have an
indistinguishable set of prints in the system’s file. The identification must always be made by a
L
final visual comparison of the suspect print’s and file print’s ridge characteristics; only these
features can impart individuality E
to a fingerprint. Although ridge patterns impart class characteristics to the print, the type and position
of ridge characteristics give it its individual character.
I
Automated
Systems
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Fingerprint
Identification
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
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The Henry system and its subclassifications
have proven to be a cumbersome system for storing,
retrieving, and searching for fingerprints,
particularly as fingerprint collections grow in size.
8
Nevertheless, until the emergence of fingerprint computer technology, this manual approach was
7
the only viable method for the maintenance of fingerprint collections. Since 1970, technological
advances have made possible the
1 classification and retrieval of fingerprints by computers.
Automated Fingerprint Identification Systems (AFISs) have proliferated throughout the law
B
enforcement community.
In 1999, the FBI initiated fullUoperation of the Integrated Automated Fingerprint Identification System (IAFIS), the largest AFIS in the United States, which links state AFIS computers
with the FBI database. This database contains nearly 50 million fingerprint records. However,
an AFIS can come in all sizes ranging from the FBI’s to independent systems operated by cities,
counties, and other agencies of local government (see Figure 16–8). Unfortunately, these local
systems often are not linked to the state’s AFIS system because of differences in software
configurations.
FINGERPRINTS
397
How AFIS Works
The heart of AFIS technology is the ability of a computer to scan and digitally encode fingerprints
so that they can be subject to high-speed computer processing. The AFIS uses automatic scanning devices that convert the image of a fingerprint into digital minutiae that contain data
showing ridges at their points of termination (ridge endings) and the branching of ridges
into two ridges (bifurcations). The relative position and orientation of the minutiae are also
determined, allowing the computer to store each fingerprint in the form of a digitally recorded
geometric pattern.
The computer’s search algorithm determines the degree of correlation between the location
and relationship of the minutiae for both the search and file prints. In this manner, a computer can
make thousands of fingerprint comparisons in a second; for example,
G a set of ten fingerprints can
be searched against a file of 500,000 ten-finger prints (ten-prints) in about eight-tenths of a second. During the search for a match, the computer uses a scoring O
system that assigns prints to each
of the criteria set by an operator. When the search is complete, the
Rcomputer produces a list of file
prints that have the closest correlation to the search prints. All of the selected prints are then
D
examined by a trained fingerprint expert, who makes the final verification
of the print’s identity.
Thus, the AFIS makes no final decisions on the identity of a fingerprint,
leaving this function to
O
the eyes of a trained examiner.
N
The speed and accuracy of ten-print processing by AFIS have made possible the search of
single latent crime-scene fingerprints against an entire file’s print, collection. Before the AFIS, police were usually restricted to comparing crime-scene fingerprints against those of known suspects. The impact of the AFIS on no-suspect cases has been dramatic. Minutes after California’s
AFIS network received its first assignment, the computer scoredJa direct hit by identifying an individual who had committed 15 murders, terrorizing the city of Los
E Angeles. Police estimate that
it would have taken a single technician, manually searching the city’s 1.7 million print cards,
S
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FIGURE 16–8
An AFIS system designed
for use by local law
enforcement agencies.
Courtesy AFIX Technologies Inc.,
Pittsburg, KS 66762, www.afix.net
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FIGURE 16–9
A side-by-side comparison of a latent print against a file fingerprint is conducted
in seconds, and their similarity rating (SIM) is displayed on the upper-left portion of
the screen.
Courtesy Sirchie Fingerprint Laboratories, Youngsville, N.C., www.sirchie.com
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CHAPTER 16
livescan
An inkless device that captures the
digital images of fingerprints and
palm prints and electronically
transmits the images to an AFIS
67 years to come up with the perpetrator’s prints. With the AFIS, the search took approximately
20 minutes. In its first year of operation, San Francisco’s AFIS computer conducted 5,514 latent
fingerprint searches and achieved 1,001 identifications—a hit rate of 18 percent. This compares
to the previous year’s average of 8 percent for manual latent-print searches.
As an example of how an AFIS computer operates, one system has been designed to automatically filter out imperfections in a latent print, enhance its image, and create a graphic representation of the fingerprint’s ridge endings and bifurcations and their direction. The print is then
computer searched against file prints. The image of the latent print and a matching file print are
then displayed side by side on a high-resolution video monitor, as shown in Figure 16–9. The
matching latent and file prints are then verified and charted by a fingerprint examiner at a video
workstation.
The stereotypical image of aG
booking officer rolling inked fingers onto a standard ten-print
card for ultimate transmission to a O
database has, for the most part, been replaced with digital-capture
devices (livescan) that eliminate ink and paper. The livescan captures the image on each finger
and the palms as they are lightly R
pressed against a glass platen. These livescan images can then
be sent to the AFIS database electronically,
so that within minutes the booking agency can enter
D
the fingerprint record into the AFIS database and search the database for previous entries of the
O
same individual. See Figure 16–10.
N
,
FIGURE 16–10
Livescan technology enables
law enforcement to print and
compare a subject’s
fingerprints rapidly, without
inking the fingerprints.
Courtesy MorphoTrak, Inc.
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FINGERPRINTS
399
Considerations with AFIS
AFIS has fundamentally changed the way criminal investigators operate, allowing them to spend
less time developing suspect lists and more time investigating the suspects generated by the computer. However, investigators must be cautioned against overreliance on a computer. Sometimes
a latent print does not make a hit because of the poor quality of the file print. To avoid these
potential problems, investigators must still print all known suspects in a case and manually search
these prints against the crime-scene prints.
AFIS computers are available from several different suppliers. Each system scans fingerprint images and detects and records information about minutiae (ridge endings and bifurcations);
however, they do not all incorporate exactly the same features, coordinate systems, or units of
measure to record fingerprint information. These software incompatibilities
often mean that,
G
although state systems can communicate with the FBI’s IAFIS, they may not communicate
O cannot share information
with each other directly. Likewise, local and state systems frequently
with each other. Many of these technical problems will be resolved
R as more agencies follow
transmission standards developed by the National Institute of Standards and Technology and
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the FBI.
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forensic brief
>>>>>>>>>>>>>>>>>
The Night Stalker
J
Richard Ramirez committed his first murder in June
E
1984. His victim was a 79-year-old woman who was
stabbed repeatedly and sexually assaulted and
S
then had her throat slashed. It would be eight
S
months before Ramirez murdered again. In the
spring, Ramirez began a murderous rampage that
I
resulted in 13 additional killings and 5 rapes.
C
His modus operandi was to enter a home
A
through an open window, shoot the male residents, and savagely rape his female victims. He
scribed a pentagram on the wall of one of his vicL
tims and the words Jack the Knife, and was reported by another to force her to “swear to Satan”
E
during the assault. His identity still unknown, the
news media dubbed him the “Night Stalker.” IAs
the body count continued to rise, public hysteria
G
and a media frenzy prevailed.
H
The break in the case came when the license
plate of what seemed to be a suspicious car related
to a sighting of the Night Stalker was reported to
1
the police. The police determined that the car had
been stolen and eventually located it, abandoned
8
in a parking lot. After processing the car for prints,
7
police found one usable partial fingerprint. This fin1
gerprint was entered into the Los Angeles Police
Department’s brand-new AFIS computerized finB
gerprint system.
U
The Night Stalker was identified as Richard
Ramirez, who had been fingerprinted following a
traffic violation some years before. Police searching
the home of one of his friends found the gun used
Richard Ramirez, the Night Stalker.
© Bettmann/CORBIS. All Rights Reserved
to commit the murders, and jewelry belonging to
his victims was found in the possession of Ramirez’s
sister. Ramirez was convicted of murder and sentenced to death in 1989. He remains on death row.
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CHAPTER 16
forensics at work
The Mayfield Affair
On March 11, 2004, a series of ten explosions at four
sites occurred on commuter trains traveling to or near
the Atocha train station in Madrid, Spain. The death toll
from these explosions was nearly 200, with more than
1,500 injured. On the day of the attack, a plastic bag was
found in a van previously reported as stolen. The bag
contained copper detonators like those used on the
train bombs. On March 17, the FBI received electronic
images of latent fingerprints that were recovered from
the plastic bag. A search was initiated on the FBI’s IAFIS.
A senior fingerprint examiner encoded seven minutiae
points from the high-resolution image of one suspect latent fingerprint and initiated an IAFIS search matching
the print to Brandon Mayfield.
Mayfield’s prints were in the FBI’s central database
because they had been taken when he joined the military,
where he served for eight years before being honorably
discharged as a second lieutenant. After a visual comparison of the suspect and file prints, the examiner concluded a “100 percent match.” The identification was
verified by a retired FBI fingerprint examiner with more
than 30 years of experience who was under contract with
the bureau, as well as by a court-appointed independent
fingerprint examiner (see Figure 16–11).
Mayfield, age 37, a Muslim convert, was arrested on
May 6 on a material witness warrant. The U.S. Attorney’s
Office came up with a list of Mayfield’s potential ties to
Muslim terrorists, which they included in the affidavit they
presented to the federal judge who ordered his arrest
and detention. The document also said that, although no
travel records were found for Mayfield, “It is believed that
Mayfield may have traveled under a false or fictitious
name.” On May 24, after the Spaniards had linked
the print from the plastic bag to an Algerian national,
Mayfield’s case was thrown out. The FBI issued him a
highly unusual official apology, and his ordeal became a
stunning embarrassment to the U.S. government.
As part of its corrective-action process, the FBI
formed an international committee of distinguished
visible print
plastic print
A fingerprint impressed in a soft
surface
,
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the power of the IAFIS match, coupled with the inherent
pressure of working an extremely high-profile case, was
thought to have influenced the initial examiner’s judgment and subsequent examination. . . . The apparent
mindset of the initial examiner after reviewing the results
of the IAFIS search was that a match did exist; therefore,
it would be reasonable to assume that the other characteristics must match as well. In the absence of a detailed
analysis of the print, it can be a short distance from finding only seven characteristics sufficient for plotting, prior
to the automated search, to the position of 12 or
13 matching characteristics once the mind-set of identification has become dominant. . . .
Once the mind-set occurred with the initial examiner,
the subsequent examinations were tainted. . . .
because of the inherent pressure of such a highprofile case, the power of an IAFIS match in conjunction with the similarities in the candidate’s print, and
the knowledge of the previous examiners’ conclusions (especially since the initial examiner was a
highly respected supervisor with many years of experience), it was concluded that subsequent examinations were incomplete and inaccurate. To disagree
was not an expected response. . . . when the individualization had been made by the examiner, it
1
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Methods of Detecting
Fingerprints
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Through common usage, the termUlatent fingerprint has come to be associated with any fingerprint discovered at a crime scene. Sometimes, however, prints found at the scene of a crime are
quite visible to the eye, and the word latent is a misnomer. Actually, there are three kinds of crimescene prints: visible prints are made by fingers touching a surface after the ridges have been in
contact with a colored material such as blood, paint, grease, or ink; plastic prints are ridge impressions left on a soft material such as putty, wax, soap, or dust; and latent or invisible prints are
impressions caused by the transfer of body perspiration or oils present on finger ridges to the
surface of an object.
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
ISBN 1-256-36593-9
A fingerprint made when the finger
deposits a visible material such as
ink, dirt, or blood onto a surface
latent-print examiners and forensic experts. Their task
was to review the analysis performed by the FBI Laboratory and make recommendations that would help
prevent this type of error in the future. The committee
came up with some startling findings and observations
G(available at www.fbi.gov/hq/lab/fsc/backissu/jan2005/
Ospecial_report/2005_special_report.htm).
The committee members agreed that “the quality
Rof the images that were used to make the erroneous
Didentification was not a factor. . . . [T]he identification is
filled with dissimilarities that were easily observed when
Oa detailed analysis of the latent print was conducted.”
N They further stated,
FINGERPRINTS
401
forensics at work
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(b)
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FIGURE 16–11
S bombing investigation. (b) File print of Brandon
(a) Questioned print recovered in connection with the Madrid
Mayfield.
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(a) Courtesy Sirchie Fingerprint Laboratories, Youngsville, NC, www.sirchie.com, U.S. Department of Justice
I
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became increasingly difficult for others in the
decision to undertake research to develop more objecA tive standards for fingerprint identification.
agency to disagree.
(a)
The committee went on to make a number of qualityassurance recommendations to help avoid a recurrence of this type of error.
The Mayfield incident has also been the subject of
an investigation by the Office of the Inspector General
(OIG), U.S. Department of Justice (www.usdoj.gov/
oig/special/s0601/final.pdf). The OIG investigation
concluded that a “series of systemic issues” in the FBI
Laboratory contributed to the Mayfield misidentification. The report noted that the FBI has made significant procedural modifications to help prevent similar
errors in the future and strongly supported the FBI’s
An internal review of the FBI Latent Print Unit
conducted in the aftermath of the Mayfield affair has
L resulted in the implementation of revisions in training,
E as well as in the decision-making process when deterthe comparative value of a latent print, along
I mining
with more stringent verification policies and procedures
G (M. A. Smrz et al., Journal of Forensic Identification
402–34).
H 56 [2006]:
The impact of the Mayfield affair on fingerprint
technology as currently practiced and the weight
1 courts will assign to fingerprint matches remain open
questions.
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Locating Fingerprints
U little problem to the invesLocating visible or plastic prints at the crime scene normally presents
tigator because these prints are usually distinct and visible to the eye. Locating latent or invisible
prints is obviously much more difficult and requires the use of techniques to make the print visible. Although the investigator can choose from several methods for visualizing a latent print, the
choice depends on the type of surface being examined.
Hard and nonabsorbent surfaces (such as glass, mirror, tile, and painted wood) require
different development procedures from surfaces that are soft and porous (such as papers, cardboard, and cloth). Prints on the former are preferably developed by the application of a powder
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CHAPTER 16
or treatment with superglue, whereas prints on the latter generally require treatment with one or
more chemicals.
Sometimes the most difficult aspect of fingerprint examination is the location of prints. Recent advances in fingerprint technology have led to the development of an ultraviolet image converter for the purpose of detecting latent fingerprints. This device, called the Reflected Ultraviolet
Imaging System (RUVIS), can locate prints on most nonabsorbent surfaces without the aid of
chemical or powder treatments (see Figure 16–12).
RUVIS detects the print in its natural state by aiming UV light at the surface suspected of
containing prints. When the UV light strikes the fingerprint, the light is reflected back to the
viewer, differentiating the print from its background surface. The transmitted UV light is then
converted into visible light by an image intensifier. Once the print is located in this manner, the
G it in the most appropriate fashion. See Figure 16–13.
crime-scene investigator can develop
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FIGURE 16–12
A Reflected Ultraviolet Imaging
CSystem allows an investigator to directly view surfaces
for the presence of untreated latent fingerprints.
Courtesy Sirchie Fingerprint Laboratories,A
Youngsville, N.C., www.sirchie.com
L
FIGURE 16–13
Using a Reflected Ultraviolet E
Imaging System with the aid ofI a
UV lamp to search for latent
G
fingerprints.
Courtesy Sirchie Fingerprint Laboratories,
Youngsville, N.C., www.sirchie.com
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#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
FINGERPRINTS
403
Developing Latent Prints
FINGERPRINT POWDERS Fingerprint powders are commercially available in a variety of compositions and colors. These powders, when applied lightly to a nonabsorbent surface with a
camel’s-hair or fiberglass brush, readily adhere to perspiration residues and/or deposits of body
oils left on the surface (see Figure 16–14).
Experienced examiners find that gray and black powders are adequate for most latent-print
work; the examiner selects the powder that affords the best color contrast with the surface being
dusted. Hence, the gray powder, composed of an aluminum dust, is used on dark-colored surfaces.
It is also applied to mirrors and metal surfaces that are polished to a mirrorlike finish because
these surfaces photograph as black. The black powder, composed basically of black carbon or
G
charcoal, is applied to white or light-colored surfaces.
Other types of powders are available for developing latent prints.
O A magnetic-sensitive powder can be spread over a surface with a magnet in the form of a Magna Brush. A Magna Brush
does not have any bristles to come in contact with the surface, soR
there is less chance that the print
will be destroyed or damaged. The magnetic-sensitive powder comes
D in black and gray and is especially useful on such items as finished leather and rough plastics, where the minute texture of
O
the surface tends to hold particles of ordinary powder. Fluorescent powders are also used to deN light. By photographing the
velop latent fingerprints. These powders fluoresce under ultraviolet
fluorescence pattern of the developing print under UV light, it is possible to avoid having the
,
color of the surface obscure the print.
IODINE FUMING Of the several chemical methods used for visualizing latent prints, iodine
fuming is the oldest. Iodine is a solid crystal that, when heated, J
is transformed into a vapor without passing through a liquid phase; such a transformation is called
E sublimation. Most often, the
suspect material is placed in an enclosed cabinet along with iodine crystals (see Figure 16–15).
S combine with constituents of
As the crystals are heated, the resultant vapors fill the chamber and
the latent print to make it visible. The reasons why latent printsSare visualized by iodine vapors
are not yet fully understood. Many believe that the iodine fumes combine with fatty oils; howI interact with residual water
ever, there is also convincing evidence that the iodine may actually
2
left on a print from perspiration.
C
Unfortunately, iodine prints are not permanent and begin to fade once the fuming process
A
is stopped. Therefore, the examiner must photograph the prints immediately on development in
order to retain a permanent record. Also, iodine-developed prints can be fixed with a 1 percent
solution of starch in water, applied by spraying. The print turnsLblue and lasts for several weeks
to several months.
iodine fuming
A technique for visualizing latent
fingerprints by exposing them to
iodine vapors
sublimation
A physical change from the solid
directly into the gaseous state
E
FIGURE
16–14
I
Developing
a latent
G
fingerprint on a surface by
H
applying
a fingerprint powder
with a fiberglass brush.
Courtesy Sirchie Fingerprint
Laboratories, Youngsville, N.C.,
www.sirchie.com
ISBN 1-256-36593-9
1
8
7
1
B
U
2
J. Almag, Y. Sasson, and A. Anati, “Chemical Reagents for the Development of Latent Fingerprints II: Controlled Addition of Water Vapor to Iodine Fumes—A Solution to the Aging Problem,” Journal of Forensic Sciences 24 (1979): 431.
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
404
CHAPTER 16
FIGURE 16–15
A heated fuming cabinet.
Courtesy Sirchie Fingerprint Laboratories,
Youngsville, N.C., www.sirchie.com
G
O
R
D
O
N
,
ninhydrin
A chemical reagent used to
develop latent fingerprints on
porous materials by reacting with
amino acids in perspiration
J
E
S
NINHYDRIN Another chemical used for visualizing latent prints is ninhydrin. The development
S
of latent prints with ninhydrin depends on its chemical reaction to form a purple-blue color with
I in perspiration. Ninhydrin (triketohydrindene hydrate) is
amino acids present in trace amounts
commonly sprayed onto the porous surface from an aerosol can. A solution is prepared by mixC
ing the ninhydrin powder with a suitable solvent, such as acetone or ethyl alcohol; a 0.6 percent
Amost applications.
solution appears to be effective for
Generally, prints begin to appear within an hour or two after ninhydrin application; however,
weaker prints may be visualized after 24 to 48 hours. The development can be hastened if the
L or on a hot plate at a temperature of 80–100°C. The ninhytreated specimen is heated in an oven
drin method has developed latentE
prints on paper as old as 15 years.
Physical Developer
A silver nitrate–based reagent
formulated to develop latent
fingerprints on porous surfaces
PHYSICAL DEVELOPER Physical
I Developer is a third chemical mixture used for visualizing
latent prints. Physical Developer is a silver nitrate–based liquid reagent. The procedure for preparG
ing and using Physical Developer is described in Appendix IV. This method has gained wide
acceptance by fingerprint examiners,
H who have found it effective for visualizing latent prints that
remain undetected by the previously described methods. Also, this technique is effective for
developing latent fingerprints on porous articles that may have been wet at one time.
1 the chemical method of choice is ninhydrin. Its extreme
For most fingerprint examiners,
sensitivity and ease of application
8 have all but eliminated the use of iodine for latent-print
visualization. However, when ninhydrin fails, development with Physical Developer may provide
identifiable results. Application of7Physical Developer washes away any traces of proteins from
an object’s surface; hence, if one
1 wishes to use all of the previously mentioned chemical
development methods on the same surface, it is necessary to first fume with iodine, follow
B then apply Physical Developer to the object.
this treatment with ninhydrin, and
Uchemical treatment for fingerprint development was reserved
In the past,
for porous surfaces such as paper and cardboard. However, since 1982, a chemical technique
known as superglue fuming has gained wide popularity for developing latent prints on nonporous surfaces such as metals, electrical tape, leather, and plastic bags.3 See Figure 16–16.
SUPERGLUE FUMING
A technique for visualizing latent
fingerprints on nonporous surfaces
by exposing them to cyanoacrylate
vapors; named for the commercial
product Super Glue.
3
F. G. Kendall and B. W. Rehn, “Rapid Method of Superglue Fuming Application for the Development of Latent
Fingerprints,” Journal of Forensic Sciences 28 (1983): 777.
#RIMINALISTICS !N)NTRODUCTIONTO&ORENSIC3CIENCE, Tenth Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2011 by Pearson Education, Inc.
ISBN 1-256-36593-9
superglue fuming
FINGERPRINTS
FIGURE 16–16
Superglue fuming a nonporous
metallic surface in the search for
latent fingerprints.
Courtesy Sirchie Fingerprint Laboratories,
Youngsville, N.C., www.sirchie.com
G
O
R
D
O
N
,
J
E
S
S
I
C
A
(a)
L
E
I
G
(b)
H
FIGURE 16–17
(a) A handheld fuming wand uses disposable cartridges containing cyanoacrylate. The
wand is used to develop prints at the crime scene and (b)1in the laboratory.
Courtesy Sirchie Fingerprint Laboratories, Youngsville, N.C., www.sirchie.com
ISBN 1-256-36593-9
8
7 a chemical that interacts with
Superglue is approximately 98–99 percent cyanoacrylate ester,
and visualizes a latent fingerprint. Cyanoacrylate ester fumes can
1 be created when superglue is
placed on absorbent cotton treated with sodium hydroxide. The fumes can also be created by heatB
ing the glue. The fumes and the evidential object are contained within an enclosed chamber for
up to six hours. Development occurs when fumes from the glue U
adhere to the latent print, usually
producing a white-appearing latent print. Interestingly, small enclosed areas, such as the interior
of an automobile, have been successfully processed for latent prints with fumes from superglue.
Through the use of a small …
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