Transcript Chapter 3 PHYSICAL EVIDENCE 3 - 1

Chapter 3
PHYSICAL EVIDENCE
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-1
Objectives
Review the common types of physical evidence encountered at
crime scenes
Explain the difference between the identification and comparison
of physical evidence
Define and contrast individual and class characteristics of physical
evidence
Appreciate the value of class evidence as it relates to a criminal
investigation
List and explain the function of national databases available to
forensic scientists
Explain the purpose physical evidence plays in reconstructing the
events surrounding the commission of a crime
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-2
http://www.youtube.com/watch?v=
awcnMrZiSmU&feature=related
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-3
Physical Evidence
• Impossible to list all the objects of
importance to a crime
• Almost anything physical evidence
• Discuss some of the most common
examples
– Collected and analyzed
– Weight unknown for given piece of evidence
– Decided by a jury
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-4
Types of Physical Evidence
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Blood, semen, and saliva
Documents
Drugs
Explosives
Fibers
Fingerprints
Firearms, ammunition
Glass
Hair
Impressions
Organs and physiological
fluids
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
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Paint
Petroleum products
Plastic bags
Plastic, rubber, and
other polymers
Powder residues
Soil and minerals
Tool marks
Vehicle lights
Wood and other
vegetative matter
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-5
• Group the types of physical evidence into
groups base on type
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-6
Key Points
• Biological crime scene evidence includes blood,
saliva semen, DNA, hair, organs
• Impression crime scene evidence includes tire
markings, shoe prints depressions in soft soil,
all other forms of tracks, glove and other fabric
impressions, tool mark and bite marks
• Manufactured items include firearms,
ammunition fibers paint glass petroleum
product plastic bags rubber polymers
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-7
The Examination of Physical
Evidence
Identification or comparison
purposes
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-8
Identification
• Items from the body for laboratory
examination
• Determine the physical or chemical
identity
• Near absolute certainty as existing
analytical techniques will permit
• Requires the adoption of testing
procedures
– Give characteristic results
– Specific standard materials
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-9
Identification
• Once test results have been
established:
– May be permanently recorded and used
repeatedly to prove the identity of
suspect materials.
• Number and type of tests needed
to identify a substance: sufficient
to exclude all other substances.
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -10
Common Types of Identification
• Chemical composition of an illicit
drug
• Gasoline in residues recovered from
the debris of a fire
• Nature of explosive residues
• Blood, semen, hair, or wood
• Species origin
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -11
Comparison
• Important role of determining common
origin.
• Both the standard/reference and the
suspect specimen subject to the same
tests
• Two-step procedure
– Combinations of select properties chosen
– Forensic scientist renders conclusion
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -12
Classifying Characteristics
Individual Characteristics
Class Characteristics
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -13
Individual Characteristics
• Not possible to state with
mathematical exactness the
probability that the specimens are
of common origin
• Only be concluded that this
probability is so high as to defy
mathematical calculations or human
comprehension
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -14
Individual Characteristics
• Ridge characteristics of two
fingerprints
• Random striation markings on
bullets or tool marks
• Irregular and random wear patterns
in tire or footwear impressions
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -15
Individual Characteristics
• Handwriting characteristics
• Irregular edges of broken objects
in the manner of a jigsaw puzzle
• Sequentially made plastic bags by
striation marks running across the
bags
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -16
Class Characteristics
• Frequent inability of laboratory to relate
physical evidence to a common origin with
a high degree of certainty
• Class characteristics
– Associated only with a group
– Never with a single source
• Probability is determining factor
• High diversity of class evidence in our
environment
• Comparison very significant in context of
a criminal investigation
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -17
Class Evidence
• Weakness: inability of the examiner to
assign exact or even approximate
probability values to comparison of most
class physical evidence
• Examples
– Nylon fiber originated from a particular
sweater
– Paint chip came from suspect car in a hit and
run
• Few statistical data available from which
to derive this information
• Gathering this kind of data is elusive
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -18
Class Evidence
• Create and update statistical databases
• Most items of physical evidence
– Cannot be linked definitively to a single
person or object
• The value of class physical evidence
– Ability to provide corroboration of events
with data
– Free of human error and bias
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -19
Class Evidence
• Chances are low
– Encountering two indistinguishable items of
physical evidence at a crime scene
– Actually originated from different sources
• More than one type of class evidence
– Collective presence may lead to an
extremely high certainty that they
originated from the same source
• Contribution of physical evidence is
ultimately determined in courtroom
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -20
Role of Probability
• Probability: frequency of
occurrence of an event
• Flipping a coin
• Analytical processes: exact
probability impossible
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -21
Crossing Over
• Crossing over the line from class to
individual
• 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, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -22
Using Physical Evidence
• Number of different objects linking
an individual to a crime scene 
• Likelihood of that individual’s
involvement with the crime 
• Person may be exonerated or
excluded from suspicion
– Physical evidence collected at crime
scene is found different from
standard/reference samples collected
from subject
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -23
Key Points
• The value of class evidence lies in its ability to
corroborate events with data in a manner that
is free of human error
• 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
• A person maybe exonerated from suspicion if
physical evidence collected is found to be
different form standard/reference samples
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -24
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, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -25
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.
• The International Forensic Automotive Paint
Data Query (PDQ) database contains
chemical and color information pertaining to
original automotive paints.
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -26
Forensic Databases
• SICAR (shoeprint image capture and
retrieval) is a shoeprint database.
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -27
Reconstruction
• Method used to support a likely sequence
of events
– Observation and evaluation of physical
evidence
– Statements made by those involved with
incident
• Relies on the combined efforts of
– Medical examiners
– Criminalists,
– Law enforcement personnel
• Recover physical evidence
• Sort out the events surrounding the
occurrence of a crime
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -28
Figure 3–6 A laser beam is used to determine the search area for the
position of a shooter who has fired a bullet through a window and
wounded a victim. The bullet path is determined by lining up the
victim’s bullet wound with the bullet hole present in the glass pane.
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -29
Role of Physical Evidence
• Crucial role in reconstructing the events
that took place surrounding the crime
• Does not describe everything that
happened
• Supports or contradicts accounts given
by witnesses and/or suspects
• Generates leads
• Confirms the reconstruction of a crime
to a jury.
• Foundation of a reconstruction
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -30
vocabulary
• class characteristics Properties of
evidence that can be associated only with
a group and never with a single source.
• comparison The process of ascertaining
whether two or more objects have a
common origin.
• identification The process of
determining a substance’s physical or
chemical identity
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -31
• individual characteristics Properties of evidence that
can be attributed to a common source with an
extremely high degree of certainty.
• product rule A formula for determining how
frequently a certain combination of characteristics
occurs in a population. The product rule states that one
must first determine the probability of each
characteristic occurring separately, then multiply
together the frequencies of all independently occurring
characteristics. The result is the overall frequency of
occurrence for that particular combination of
characteristics.
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -32
• reconstruction The method used to
support a likely sequence of events at a
crime scene by observing and evaluating
physical evidence and statements made
by those involved with the incident.
•
CRIMINALISTICS
An Introduction to Forensic Science, 9/E
By Richard Saferstein
PRENTICE HALL
©2007 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3 -33