Transcript Document

Chapter 1
INTRODUCTION
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-1
Definition
• In its broadest definition, forensic science is the
application of science to criminal and civil laws.
• The subject matter of this book emphasizes the
application of science to those criminal and
civil laws that are enforced by police agencies
in a criminal justice system.
• Forensic science owes its origins to individuals
such as Bertillon, Galton, Lattes, Goddard,
Osborn, and Locard, who developed the
principles and techniques needed to identify or
compare physical evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-2
History
• Mathieu Orfila—the father of forensic toxicology.
• Alphonse Bertillion—devised the first scientific
system of personal identification in 1879.
• Francis Galton—conducted the first definitive
study of fingerprints and their classification.
• Leone Lattes—developed a procedure to
determine blood type from dried bloodstains.
• Calvin Goddard—used a comparison microscope
to determine if a particular gun fired a bullet.
• Albert Osborn—developed the fundamental
principles of document examination.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-3
History
• Walter McCrone—utilized microscopy and other
analytical methodologies to examine evidence.
• Hans Gross—wrote the first treatise describing the
application of scientific principles to the field of
criminal investigation.
• Edmond Locard—incorporared Gross’ principles
within a workable crime laboratory.
• Locard’s Exchange Principle—states that when a
criminal comes in contact with an object or
person, a cross-transfer of evidence occurs.
• Sir Alec Jeffreys—developed the first DNA
profiling test in 1984.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-4
The Crime Lab
• The development of crime laboratories in
the United States has been characterized
by rapid growth accompanied by a lack
of national and regional planning and
coordination.
• At present, approximately 350 public
crime laboratories operate at various
levels of government—federal, state,
county, and municipal.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-5
The Crime Lab
• The ever increasing number of crime
laboratories is partly the result of the
following:
– Supreme Court decisions in the 1960s
responsible for police placing greater
emphasis on scientifically evaluated
evidence.
– Crime laboratories inundated with drug
specimens due to accelerated drug abuse.
– The advent of DNA profiling.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-6
Technical Support
• The technical support provided by crime
laboratories can be assigned to five basic
services.
– Physical Science Unit incorporates the
principles of chemistry, physics, and geology
to identify and compare physical evidence.
– Biology Unit applies the knowledge of
biological sciences in order to investigate
blood samples, body fluids, hair, and fiber
samples.
– Firearms Unit investigates discharged
bullets, cartridge cases, shotgun shells, and
ammunition.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-7
Technical Support
– Document Unit provides the skills needed for
handwriting analysis and other questioneddocument issues.
– Photographic Unit applies specialized
photographic techniques for recording and
examining physical evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-8
Technical Support
• Optional Services by Full-Service Labs
– Toxicology Unit examines body fluids and organs for
the presence of drugs and poisons.
– Latent Fingerprint Unit processes and examines
evidence for latent fingerprints.
– Polygraph Unit conducts polygraph or lie detector
tests.
– Voiceprint Analysis Unit attempts to tie a recorded
voice to a particular suspect.
– Evidence-Collection Unit dispatches specially
trained personnel to the crime scene to collect and
preserve physical evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-9
The Scientific Method
• Formulate a question worthy of
investigation.
• Formulate a reasonable hypothesis to
answer the question.
• Test the hypothesis through
experimentation.
• Upon validation of the hypothesis, it
become suitable as scientific evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-10
Skills of a Forensic Scientist
• A forensic scientist must be skilled in applying
the principles and techniques of the physical
and natural sciences to the analysis of the many
types of evidence that may be recovered during
a criminal investigation.
• A forensic scientist may also provide expert
court testimony.
• An expert witness is an individual whom the
court determines possesses knowledge relevant
to the trial that is not expected of the average
person.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-11
Skills of a Forensic Scientist
• The expert witness is called on to
evaluate evidence based on specialized
training and experience that the court
lacks the expertise to do.
• The expert will then express an opinion
as to the significance of the findings.
• Forensic scientists also participate in
training law enforcement personnel in
the proper recognition, collection, and
preservation of physical evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-12
The Frye Standard
• The Frye v. United States decision set guidelines
for determining the admissibility of scientific
evidence into the courtroom.
• To meet the Frye standard, the evidence in
question must be “generally accepted” by the
scientific community.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-13
Frye Not Absolute
• However, in the 1993 case of Daubert v.
Merrell Dow Pharmaceutical, Inc., the
U.S. Supreme Court asserted that the
Frye standard is not an absolute
prerequisite to the admissibility of
scientific evidence.
• Trial judges were said to be ultimately
responsible as “gatekeepers” for the
admissibility and validity of scientific
evidence presented in their courts, as well
as all expert testimony.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-14
Daubert Criteria For Admissibility
• Whether the scientific technique or
theory can be tested.
• Whether the technique has been subject
to peer review and publication.
• The techniques potential rate of error.
• Existence and maintenance of standards .
• Whether the scientific theory or method
has attracted widespread acceptance
within a relevant scientific community.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-15
Special Forensic Science Services
• A number of special forensic science
services are available to the law
enforcement community to augment the
services of the crime laboratory.
• These services include forensic pathology,
forensic anthropology, forensic
entomology, forensic psychiatry, forensic
odontology, computer science, and
forensic engineering.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-16
Special Forensic Science Services
• Forensic Psychiatry is an area in which the relationship
between human behavior and legal proceedings is
examined.
• Forensic Odontology involves using teeth to provide
information about the identification of victims when a
body is left in an unrecognizable state. Also
investigates bite marks.
• Forensic Engineering is concerned with failure analysis,
accident reconstruction, and causes and origins of fires
or explosions.
• Forensic Computer Science involves the examination of
digital evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-17
Chapter 2
THE CRIME SCENE
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-18
Physical Evidence
• As automobiles run on gasoline, crime
laboratories “run” on physical evidence.
• Physical evidence encompasses any and all
objects that can establish that a crime has been
committed or can provide a link between a
crime and its victim or a crime and its
perpetrator.
• But if physical evidence is to be used effectively
for aiding the investigator, its presence first
must be recognized at the crime scene.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-19
The Beginning
• Forensic science begins at the crime scene.
• If the investigator cannot recognize physical
evidence or cannot properly preserve it for
laboratory examination, no amount of
sophisticated laboratory instrumentation or
technical expertise can salvage the situation.
• Here, investigators must recognize and properly
preserve evidence for laboratory examination.
• It must be emphasized that the techniques of
crime-scene investigation are not difficult to
master and certainly lie within the bounds of
comprehension of the average police officer.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-20
The First Steps
• The first officer to arrive at the scene is
responsible for securing the crime scene.
• First priority should be given to obtaining
medical assistance for individuals in need of it
and to arresting the perpetrator.
• As soon as it is possible, extensive efforts must
be made to exclude all unauthorized personnel
from the scene.
• Once the scene is secured, the preliminary
exam must begin.
• Recording of the crime scene becomes a critical
piece to the investigation process.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-21
Recording Methods
• Photography, sketches, and notes are the
three methods for crime-scene recording.
• Ideally all three should be employed;
however, as is often the case, personnel
and monetary limitations may prohibit
the utilization of photography at every
crime site.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-22
Photography
• The most important prerequisite for
photographing a crime scene is for it to be in an
unaltered condition.
• Unless there are injured parties involved, objects
must not be moved until they have been
photographed from all necessary angles.
• As items of physical evidence are discovered, they
are photographed to show their position and
location relative to the entire scene.
• After these overviews are taken, close-ups should
be taken to record the details of the object itself.
– When the size of an item is of significance, a ruler or
other measuring scale may be inserted near the object
and included in the photograph as a point of reference.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-23
Sketches
• Once photographs are taken, the crime-scene
investigator will sketch the scene.
• Rough Sketch—A draft representation of all
essential information and measurements at a
crime scene. This sketch is drawn at the crime
scene. It shows all recovered items of physical
evidence, as well as other important features of
the crime scene.
• Finished Sketch—A precise rendering of the
crime scene, usually drawn to scale. This type is
not normally completed at the crime scene.
• Unlike the rough sketch, the finished sketch is
drawn with care and concern for aesthetic
appearance.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-24
Notes
• Note taking must be a constant activity
throughout the processing of the crime scene.
• These notes must include a detailed written
description of the scene with the location of items
of physical evidence recovered.
• They must identify:
–
–
–
–
the time an item of physical evidence was discovered.
by whom.
how and by whom it was packaged and marked.
the disposition of the item after it was collected.
• The note taker has to keep in mind that this
written record may be the only source of
information for refreshing one’s memory.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-25
Recording the Crime Scene
• Investigators have only a limited amount of
time to work a crime site in its untouched state.
• The opportunity to permanently record the
scene in its original state must not be lost.
• Such records will not only prove useful during
the subsequent investigation but are also
required for presentation at a trial in order to
document the condition of the crime site and to
delineate the location of physical evidence.
• Every step of the investigation should be
documented thoroughly with an appropriate
method.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-26
The Preliminary Exam
• A lead investigator will start the process of evaluating
the area.
– First, the boundaries of the scene must be
determined
– Followed by the establishment of the perpetrator’s
path of entry and exit.
– The investigator then proceeds with an initial
walk-through of the scene to gain an overview of
the situation and develop a strategy for the
systematic examination and documentation of the
entire crime scene.
• This is done before processing the crime scene for
physical evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-27
The Search
• The search for physical evidence at a crime
scene must be thorough and systematic.
• The search pattern selected will normally
depend on the size and locale of the scene and
the number of collectors participating in the
search.
• For a factual, unbiased reconstruction of the
crime, the investigator, relying upon his or her
training and experience, must not overlook any
pertinent evidence.
• Physical evidence can be anything from
massive objects to microscopic traces.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-28
The Search
• Often, many items of evidence are clearly
visible but others may be detected only
through examination at the crime
laboratory.
• For this reason, it is important to collect
possible carriers of trace evidence, such
as clothing, vacuum sweepings, and
fingernail scrapings, in addition to more
discernible items.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-29
Beyond the Crime Scene
• The search for physical evidence must extend
beyond the crime scene to the autopsy room of
a deceased victim.
• Here, the medical examiner or coroner will
carefully examine the victim to establish a
cause and manner of death.
• As a matter of routine, tissues and organs will
be retained for pathological and toxicological
examination.
• At the same time, arrangements must be made
between the examiner and investigator to
secure a variety of items that may be obtainable
from the body for laboratory examination.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-30
Beyond The Crime Scene
• The following are to be collected and sent to the
forensic laboratory:
1. Victim’s clothing
2. Fingernail scrapings
3. Head and pubic hairs
4. Blood (for DNA typing purposes)
5. Vaginal, anal, and oral swabs (in sexrelated crimes)
6. Recovered bullets from the body
7. Hand swabs from shooting victims
(for gunshot residue analysis)
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Packaging
• Each different item or similar items collected at
different locations must be placed in separate
containers. Packaging evidence separately
prevents damage through contact and prevents
cross-contamination.
• The well-prepared evidence collector will arrive
at a crime scene with a large assortment of
packaging materials and tools ready to
encounter any type of situation.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-32
Packaging
• Forceps and similar tools may have to be used to
pick up small items.
• Unbreakable plastic pill bottles with pressure lids
are excellent containers for hairs, glass, fibers,
and various other kinds of small or trace
evidence.
• Alternatively, manila envelopes, screw-cap glass
vials, or cardboard pillboxes are adequate
containers for most trace evidence encountered at
crime sites.
• Ordinary mailing envelopes should not be used as
evidence containers because powders and fine
particles will leak out of their corners.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-33
Packaging
• Small amounts of trace evidence can also be
conveniently packaged in a carefully folded
paper, using what is known as a “druggist
fold.”
• Although pill bottles, vials, pillboxes, or manila
envelopes are good universal containers for
most trace evidence, two frequent finds at
crime scenes warrant special attention.
• If bloodstained materials are stored in airtight
containers, the accumulation of moisture may
encourage the growth of mold, which can
destroy the evidential value of blood.
• In these instances, wrapping paper, manila
envelopes, or paper bags are recommended
packaging materials.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Chain of Custody
• Chain of Custody—A list of all persons who
came into possession of an item of evidence.
• Continuity of possession, or the chain of
custody, must be established whenever evidence
is presented in court as an exhibit.
• Adherence to standard procedures in recording
the location of evidence, marking it for
identification, and properly completing
evidence submission forms for laboratory
analysis is critical to chain of custody.
• This means that every person who handled or
examined the evidence and where it is at all
times must be accounted for.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-35
Obtaining Reference Samples
• Standard/Reference Sample—Physical evidence
whose origin is known, such as blood or hair
from a suspect, that can be compared to crimescene evidence.
• The examination of evidence, whether it is soil,
blood, glass, hair, fibers, and so on, often
requires comparison with a known
standard/reference sample.
• Although most investigators have little
difficulty recognizing and collecting relevant
crime-scene evidence, few seem aware of the
necessity and importance of providing the
crime lab with a thorough sampling of
standard/reference materials.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-36
Special Forensic Science Services
• Forensic Pathology involves the
investigation of unnatural, unexplained,
or violent deaths.
– Forensic pathologists in their role as medical
examiners or coroners are charged with
determining cause of death.
– The forensic pathologist may conduct an
autopsy which is the medical dissection and
examination of a body in order to determine
the cause of death.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-37
Special Forensic Science Services
• After a human body expires there are several
stages of death.
– Rigor mortis results in the shortening of muscle
tissue and the stiffening of body parts in the position
at death (occurs within the first 24 hrs. and
disappears within 36 hrs.).
– Livor mortis results in the settling of blood in areas
of the body closest to the ground (begins
immediately on death and continues up to 12 hrs.).
– Algor mortis results in the loss of heat by a body (a
general rule, beginning about an hour after death,
the body loses heat by 1 to 1 1/2 degrees Fahrenheit
per hour until the body reaches the environmental
temperature).
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-38
Special Forensic Science Services
• Forensic Anthropology is concerned
primarily with the identification and
examination of human skeletal remains.
• Forensic Entomology is the study of
insects and their relation to a criminal
investigation, commonly used to estimate
the time of death.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-39
Chapter 3
PHYSICAL EVIDENCE
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-40
Physical Evidence
• It would be impossible to list all the objects that
could conceivably be of importance to a crime.
• Almost anything can be Physical Evidence.
• Although you cannot rely on a list of categories,
it is useful to discuss some of the most common
types of physical evidence.
• The purpose of recognizing physical evidence is
so that it can be collected and analyzed.
• It is difficult to ascertain the weight a given
piece of evidence will have in a case as
ultimately the weight will be decided by a jury.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-41
Types of Physical Evidence
•
•
•
•
•
•
•
•
•
•
•
Blood, semen, and saliva
Documents
Drugs
Explosives
Fibers
Fingerprints
Firearms and
ammunition
Glass
Hair
Impressions
Organs and physiological
fluids
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
•
•
•
•
•
•
•
•
•
Paint
Petroleum products
Plastic bags
Plastic, rubber, and other
polymers
Powder residues
Soil and minerals
Tool marks
Vehicle lights
Wood and other
vegetative matter
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Purpose of Examining Physical Evidence
• The examination of physical evidence by a
forensic scientist is usually undertaken for
identification or comparison purposes.
• Identification has, as its purpose, the
determination of the physical or chemical
identity of a substance with as near absolute
certainty as existing analytical techniques will
permit.
• A comparison analysis subjects a suspect
specimen and a standard/reference specimen to
the same tests and examinations for the ultimate
purpose of determining whether or not they have
a common origin.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Identification
• The object of an identification is to determine the
physical or chemical identity with as near absolute
certainty as existing analytical techniques will permit.
– The process of identification first requires the
adoption of testing procedures that give
characteristic results for specific standard materials.
– Once these test results have been established, they
may be permanently recorded and used repeatedly
to prove the identity of suspect materials.
– Second, identification requires that the number and
type of tests needed to identify a substance be
sufficient to exclude all other substances.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Common Types of Identification
• The crime laboratory is frequently requested to
identify the chemical composition of an illicit
drug.
• It may be asked to identify gasoline in residues
recovered from the debris of a fire, or it may
have to identify the nature of explosive
residues—for example, dynamite or TNT.
• The identification of blood, semen, hair, or
wood are also very common and, as a matter of
routine, include a determination for species
origin.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Comparison
• A comparative analysis has the important role
of determining whether or not a suspect
specimen and a standard/reference specimen
have a common origin.
• Both the standard/reference and the suspect
specimen are subject to the same tests.
• The forensic comparison is actually a two-step
procedure.
– First, combinations of select properties are chosen
from the suspect and the standard/reference
specimen for comparison.
– Second, once the examination has been completed,
the forensic scientist must be prepared to render a
conclusion with respect to the origins.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Role of Probability
• To comprehend the evidential value of a
comparison, one must appreciate the role
that probability has in ascertaining the
origins of two or more specimens.
• Simply defined, probability is the
frequency of occurrence of an event.
• In flipping a coin, probability is easy to
establish.
• With many analytical processes exact
probability is impossible to define.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Classifying Characteristics
• Individual Characteristics
– Evidence that can be associated to a
common source with an extremely high
degree of probability is said to possess
individual characteristics.
• Class Characteristics
– Evidence associated only with a group
is said to have class characteristics.
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An Introduction
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©2008 Pearson Education, Inc.
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Individual Characteristics
• In all cases, it is not possible to state with
mathematical exactness the probability
that the specimens are of common origin.
• It can only be concluded that this
probability is so high as to defy
mathematical calculations or human
comprehension.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Individual Characteristics
• Examples:
– the matching ridge characteristics of two
fingerprints
– the comparison of random striation markings on
bullets or tool marks
– the comparison of irregular and random wear
patterns in tire or footwear impressions
– the comparison of handwriting characteristics
– the fitting together of the irregular edges of broken
objects in the manner of a jigsaw puzzle
– matching sequentially made plastic bags by striation
marks running across the bags
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Class Characteristics
• Surprising to the inexperienced forensic
scientist is the frequent inability of the
laboratory to relate physical evidence to a
common origin with a high degree of certainty.
• Evidence is said to possess class characteristics
when it can be associated only with a group and
never with a single source.
• Here again, probability is a determining factor.
• Nevertheless, the high diversity of class
evidence in our environment makes their
comparison very significant in the context of a
criminal investigation.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Class Evidence
• One of the current weaknesses of forensic
science is the inability of the examiner to assign
exact or even approximate probability values to
the comparison of most class physical evidence.
• For example, what is the probability that a
nylon fiber originated from a particular
sweater, or that a paint chip came from a
suspect car in a hit and run?
• There are very few statistical data available
from which to derive this information, and in a
mass-produced world, gathering this kind of
data is increasingly elusive.
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An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
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Class Evidence
• One of the primary endeavors of forensic
scientists must be to create and update
statistical databases for evaluating the
significance of class physical evidence.
• Most items of physical evidence retrieved at
crime scenes cannot be linked definitively to a
single person or object.
• The value of class physical evidence lies in its
ability to provide corroboration of events with
data that are, as nearly as possible, free of
human error and bias.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-53
Class Evidence
• The chances are low of encountering two
indistinguishable items of physical evidence at
a crime scene that actually originated from
different sources.
• When one is dealing with more than one type
of class evidence, their collective presence
may lead to an extremely high certainty that
they originated from the same source.
• Finally, the contribution of physical evidence
is ultimately determined in the courtroom.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-54
Crossing Over
• Crossing over the line from class to individual
does not end the discussions.
• How many striations are necessary to
individualize a mark to a single tool and no
other?
– How many color layers individualize a paint chip to
a single car?
– How many ridge characteristics individualize a
fingerprint?
– How many handwriting characteristics tie a person
to a signature?
• These are all questions that defy simple
answers and are the basis of arguments.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-55
Natural vs. Evidential Limits
• There are practical limits to the properties and
characteristics the forensic scientist can select
for comparison.
– Modern analytical techniques have become
so sophisticated and sensitive that natural
variations in objects become almost infinite.
– Carrying natural variations to the extreme,
no two things in this world are alike in every
detail.
– Evidential variations are not the same as
natural variations.
– Distinguishing variations of evidential use
from natural variations is not always an easy
task.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-56
Using Physical Evidence
• As the number of different objects linking an
individual to a crime scene increases, so does
the likelihood of that individual’s involvement
with the crime.
• Just as important, a person may be exonerated
or excluded from suspicion if physical evidence
collected at a crime scene is found to be
different from standard/reference samples
collected from that subject.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-57
Forensic Databases
• The Integrated Automated Fingerprint Identification System
(IAFIS), a national fingerprint and criminal history system
maintained by the FBI.
• TheCombined DNA Index System (CODIS) enables federal, state,
and local crime laboratories to electronically exchange and
compare DNA profiles.
• The National Integrated Ballistics Information Network (NIBIN)
allows firearm analysts to acquire, digitize, and compare markings
made by a firearm on bullets and cartridge casings.
• The International Forensic Automotive Paint Data Query (PDQ)
database contains chemical and color information pertaining to
original automotive paints.
• SICAR (shoeprint image capture and retrieval) is a shoeprint
database.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-58
Reconstruction
• The method used to support a likely sequence
of events by the observation and evaluation of
physical evidence, as well as statements made
by those involved with the incident, is referred
to as reconstruction.
• Crime-scene reconstruction relies on the
combined efforts of medical examiners,
criminalists, and law enforcement personnel to
recover physical evidence and to sort out the
events surrounding the occurrence of a crime.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-59
The Role of Physical Evidence
• The physical evidence left behind at a crime
scene plays a crucial role in reconstructing the
events that took place surrounding the crime.
• Although the evidence alone does not describe
everything that happened, it can support or
contradict accounts given by witnesses and/or
suspects.
• Information obtained from physical evidence
can also generate leads and confirm the
reconstruction of a crime to a jury.
• The collection and documentation of physical
evidence is the foundation of a reconstruction.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-60
Summing It Up
• Reconstruction is a team effort that involves
putting together many different pieces of a
puzzle.
• The right connections have to be made among all
the parts involved so as to portray the
relationship among the victim, the suspect, and
the crime scene.
• If successful, reconstruction can play a vital role
in aiding a jury to arrive at an appropriate
verdict.
• The recognition, collection, and analysis of
physical evidence is the foundation to successful
reconstruction, but only part of the process.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
1-61