Do now: What type
of information can an
expert witness offer?
THE CASE:
A fleet of U.S. naval vessels in heading due north
into frigid Arctic waters when it comes under
heavy enemy attack. One member of the flotilla
sinks to the bottom and disappears from enemy
radar screens. Although the captain and the
entire crew went down with the ship, the rest of
the fleet does not stop to look for survivors.
THE MYSTERY:
What type of ship sank to the bottom and how
many crew members were killed?
CLUES:
The crew couldn’t survive for long in the cold
Arctic waters.
No crew member was found in the water.
The crew was prepared for what happened.
The ship went hundreds of feet below the surface.
The ship had sunk before.
The ship continued its voyage as planned.
Properties of
Physical Evidence
Aim: How is physical
evidence broken down
in to different
categories?
Physical Evidence Analysis

Class Characteristics
– a. Describe the physical object and limit (but not
eliminate) the likelihood that similar objects exist.
– b. The greater the number of class characteristics
that can be associated with a given object, the
smaller the category within which the object can
be placed.
– c. The larger the number of class characteristics,
the greater the value in an investigation.
– d. Physical evidence with class characteristics may
have more than one possible source.

Individual/Identification Characteristics of
Physical Evidence
– a. Establish a physical object's
difference/uniqueness from all others within its
group.
– b. Establish the unique identity of an object or its
source to the exclusion of all others.
Ballistic
examinations
Mathematical Probability

The probability of any given occurrence at
a specific place or time relates to the
value of a piece of physical evidence.
– Example: The likelihood of two different people
sharing an exact print (type, characteristics,
spatial and planer relationship) is 1:10.
The less frequent the rate or probability of
independent occurrences, the firmer the
base of confidence becomes.
 The greater the frequency of an
occurrence, the less significance that can
be attached to its evidentiary value.







1969 yellow VW Beetle is observed in commission
of a hit and run in 1969.
In 1969, yellow VW Beetles were common
(popular car, limited color selection).
The chances were greater that two yellow 1969
VW Beetles could exist in the same vicinity in
1969 than today.
Therefore, this information may lack significance
in 1969.
1969 yellow VW Beetle is observed in commission
of a hit and run in 2001.
1969 yellow VW's (and VW's in general) are less
common in 2001.
Therefore, the rate of occurrence of the presence
of a yellow VW Beetle would be significantly less.
Thus, the odds (mathematical probability) would
favor such a vehicle being the suspect vehicle if
found in the vicinity/jurisdiction where the hit
and run occurred.
The presence of fresh damage would also impact
the odds.
Major Groupings Of Physical
Evidence
 a.
Physical evidence is any
material, however microscopic,
solid, liquid or gaseous, that may
aid in the determination of the
truth during the investigation of
a crime.
 b. Physical evidence capable of
scientific analysis that is likely to
be found at the scene of a crime
falls into eight (8) major groups
and one (1) miscellaneous group.
(1) Weapons - I.D. Knife wounds
(2) Blood, saliva, and semen - I.D.
(3) Latent impressions - I.D.
(4) Shoe and tire impressions - I.D.
(5) Tool Marks - I.D.
(6) Questioned documents - Class to I.D.
(7) Soil - Class
(8) Glass – Class
(9) Miscellaneous trace evidence such as
hair, fibers, paint chips, and bomb
residue - Class