Transcript Document

Chapter 3
PHYSICAL EVIDENCE
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-1
Physical Evidence
Objectives:
1. Review the common types of physical
evidence encountered at a crime scene
2. Explain the difference between the
identification and comparison of
physical evidence.
3. Define and contrast individual and class
characteristics of physical evidence.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-2
Green River Killer
YouTube - Gary Ridgway'Green River
Killer' Part 1 of 5
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-3
Types of Physical Evidence
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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
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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
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-4
Purpose of Examining Physical Evidence
• Physical evidence is examined for
identification or comparison purposes.
• Identification – the process of
determining a substance’s physical or
chemical identity
• Comparison – the process of ascertaining
whether two or more objects have a
common origin
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-5
Identification Examples
• Chemical compositions of substances that
are illicit drugs.
• Residue from a fire or explosion
• identification of blood, semen, hair, or
wood
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-6
Comparison Examples
• A hair found at a crime scene
may match a hair sample taken
from a suspect
• A paint chip found on a hit-andrun victim’s clothing may match
paint taken from s suspects
vehicle
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-7
Comparison Characteristics
• Individual Characteristics
– Evidence that can be associated to a
common single source with an
extremely high degree of probability
• Never 100 % certain
• High degree of probability
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-8
Individual Characteristics
• Examples:
– fingerprints
– random striation markings on bullets or tool
marks
– irregular and random wear patterns in tire
or footwear impressions
– handwriting characteristics
– the fitting together of the irregular edges of
broken objects as in a jigsaw puzzle
– matching sequentially made plastic bags by
striation marks running across the bags
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-9
Class Characteristics
• Class Characteristics
-evidence that can be associated only with a
group and not with a single source
• Examples:
-Blood types
-Paint from a car
-clothing fibers
-carpet fibers
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-10
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
3-11
Forensic Databases
• IAFIS-The Integrated Automated Fingerprint Identification
System; a national fingerprint and criminal history system
maintained by the FBI. (1999)
• CODIS – The Combined DNA Index System; enables federal,
state, and local crime laboratories to electronically exchange and
compare DNA profiles; maintained by FBI (1998)
• NIBIN - The National Integrated Ballistics Information
Network; allows firearm analysts to acquire, digitize, and
compare markings made by a firearm on bullets and cartridge
casings. (ATF)
• PDQ - The International Forensic Automotive Paint Data
Query; database contains chemical and color information
pertaining to original automotive paints. (RCMP)
• SICAR - shoeprint image capture and retrieval; a shoeprint
database.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-12
Physical Evidence
Objective:
• Explain the purpose physical evidence
plays in reconstructing the events
surrounding the commission of a crime.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-13
Crime Scene Reconstruction
• 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
• The collection and documentation of physical
evidence plays a crucial role in reconstructing
the events that took place surrounding the
crime.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-14
Crime Scene Reconstruction
Who is involved in reconstruction?
• Medical examiners
• Criminalists/crime scene investigators
• Law enforcement
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-15
Reconstruction Examples
• Determining whether a body was moved after
death
• Determining whether a victim was clothed at
the time of death
• Analyzing bullet trajectory
• Analyzing blood spatter
• Determining the direction from which
projectiles penetrated glass objects
• Estimating distance of a shooter from a target
• Locating gunshot residues on a suspect
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
3-16