Transcript Physical Evidence

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.
• Almost anything can be 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.
All Rights Reserved
Types of Physical Evidence
•
•
•
•
•
•
•
•
•
•
Blood, semen, and saliva
Documents
Drugs
Hair
Impressions
Organs and physiological
fluids
Paint
Petroleum products
Powder residues
Soil and minerals
Explosives
Fibers
Fingerprints
Firearms and ammunition
Glass
Plastic bags
Plastic, rubber, and other
polymers
• Wood and other vegetative
matter
• Tool marks
• Vehicle lights
•
•
•
•
•
•
•
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
Identification….
 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 chemical composition of an illicit
drug.
• identify gasoline in residues recovered
from the debris of a fire,
• 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
Wood
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.
• 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.
All Rights Reserved
Classifying Characteristics
• Individual Characteristics
 Evidence that can be associated to a
common source with an extremely high
degree of probability
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
All Rights Reserved
Individual Characteristics
• Examples:
 The matching ridge characteristics of
two fingerprints
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
 The comparison of random striation
markings on bullets or tool marks
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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
 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.
All Rights Reserved
• 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.
All Rights Reserved
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
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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.
All Rights Reserved
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.
All Rights Reserved
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.
• 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.
All Rights Reserved
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
From Class to Individual
• How much information (testing) is
needed for evidence to go from class to
individual classification (crossing over)?
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved
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
• Limits to 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.
 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
Reconstruction
• Upon analysis of evidence it may be necessary to
reconstruct the crime scene
 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.
Criminalistics: An Introduction to Forensic Science, 11e
Richard Saferstein
Copyright © 2011 by Pearson Education, Inc.
All Rights Reserved