Transcript individual characteristics

Criminalistics
An Introduction to Forensic Science
ELEVENTH EDITION
CHAPTER
3
Physical Evidence
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2015 by Pearson Education, Inc.
All Rights Reserved
Physical Evidence
• Physical evidence encompasses any
and all objects that can establish that a
crime has or has not been committed
or can provide a link between a crime
and its victim or a crime and its
perpetrator.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Physical Evidence
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Types of Physical Evidence
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Blood, semen, and saliva
Documents
Drugs
Explosives
Fibers
Fingerprints
Firearms and ammunition
Glass
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
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Types of Physical Evidence
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Hair
Impressions
Organs and physiological fluids
Paint
Petroleum products
Plastic bags
Plastic, rubber, and other polymers
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
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Types of Physical Evidence
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Powder residues
Soil and minerals
Tool marks
Vehicle lights
Wood and other vegetative matter
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
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Purpose of Examining Physical
Evidence
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
 Once these test results have been
established, they may be permanently
recorded and used repeatedly to prove
the identity of suspect materials.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
 Second, identification requires that the
number and type of tests needed to
identify a substance be sufficient to
exclude all other substances.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Common Types of Identification
• The identification of blood, semen, hair,
or wood are also very common and as a
matter of routine, include a
determination for species origin.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Comparison
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
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Role of Probability
• In flipping a coin, probability is easy to
establish.
• With many analytical processes exact
probability is impossible to define.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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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
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Individual Characteristics
• Examples:
 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
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Class Characteristics
• Class Characteristics
 Evidence associated only with a group is
said to have class characteristics.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
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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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Class 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Class Evidence
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Class Evidence
• The chances are low of encountering
two indistinguishable items of physical
evidence at a crime scene that actually
originated from different sources.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Class Evidence
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Crossing Over
• Crossing over the line from class to
individual does not end the discussions.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
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Crossing Over
• 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?
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Crossing Over
• These are all questions that defy simple
answers and are the basis of
arguments.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Natural vs. Evidential Limits
• There are practical limits to the
properties and characteristics the
forensic scientist can select for
comparison.
 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Natural vs. Evidential Limits
• There are practical limits to the
properties and characteristics the
forensic scientist can select for
comparison.
 Distinguishing variations of evidential
use from natural variations is not
always an easy task.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Using Physical Evidence
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Forensic Databases
• The Integrated Automated Fingerprint
Identification System (IAFIS), a
national fingerprint and criminal history
system maintained by the FBI.
• The Combined DNA Index System
(CODIS) enables federal, state, and
local crime laboratories to electronically
exchange and compare DNA profiles.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Forensic Databases
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Forensic Databases
• 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved