Download Chapter 3 – Physical Evidence I. Analysis of physical evidence

Chapter 3 – Physical Evidence
I. Analysis of physical evidence
Physical evidence is: Any or 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; anything
that is tangible, can be seen or measured, with or without
magnification.
Types:
1. Blood, semen, and saliva
2. Documents
3. Drugs
4. Explosives
5. Fibers
6. Fingerprints
7. Firearms and ammunition
8. Glass
9. Hair
10.
Impressions (teeth,
tools,…)
11.
Organs and
physiological fluids
12.
Paint
13.
Petroleum products
14.
Plastic bags
15.
Powder residues
16.
Serial numbers
17.
Soil and minerals
18.
Tool marks
19.
Vehicle lights
20.
Wood and vegetative
matter
II. Two reasons to exam physical evidence 1. Identification – Source of physical evidence = body, crime
scene, suspect
2. Comparison
Characteristics:
a. Individual: can be identified with a particular
person or source (DNA; Fingerprints, random
striations)
b. Class: common to a group of objects or
persons (Levi blue jeans; white paint, green
carpet,…)
III. The Significance of Physical Evidence
A. Assessing the value of physical evidence.
1. Class evidence is not unique.
2. Can compare chemical and physical properties.
3. More than one type of class evidence can lead to
extremely high certainty.
B. Maintain Chain of Custody –continuity of possession
of evidence; adhere to standard procedures in recording the
location of evidence, marking it for identification, and properly
completing evidence submission forms for lab analysis. EVERY
person who handled or examined the evidence MUST be
accounted for.
Physical evidence is accorded great weight by juries and
scientists are held in high esteem so great care must be given
to make sure that scientific evidence is not handled
inappropriately and therefore give doubt in the case.
IV. Forensic Databases
A. Fingerprint Databases – IAFIS (Integrated Automated
Fingerprint Identification System). A national fingerprint and
criminal history system maintained by the FBI. Started in 1999,
now has 50 million subjects and 500 million fingerprint images.
B. DNA Databases – 1998, FBI’s Combined DNA Index System
(CODIS). The forensic index contains about 110,000 profiles from
unsolved crime-scene evidence; the offender index contains the
profiles of 7 million convicted or arrested individuals. In a typical
month, matches are found linking suspects to 26 murders, 57
rapes, and 3000 motor vehicle, property and drug crimes.