Chapter Two
The Nature of Evidence
oThe physical evidence recovered from any scene will, based on its nature, provide:
Class characteristics
Individual characteristics
Or both
oClass Characteristics
A trait or characteristic that allows the item to be compared with another
group of items to be compared with another group of items and included or
excluded in the group
Characteristics include size, color, manufacturing patterns, etc
A series of properties that allows inclusion or exclusion.
Can’t individualize to the exclusion of all others
Example:
Hair
oCan typically identify general body part, color, or race
oIndividual Characteristics
A trait or characteristic that allows the item to be compared to an individual
item or person
Identifies specific individual to exclusion of all others
Example:
Fingerprints and DNA can identify the specific individual who
deposited the print or body fluid
Basic forensic concepts
oLocard’s principle of exchange
Every contact leaves its trace
Finger prints and DNA
Whenever two objects come into contact with one another, material from the
first is transferred to the second, and material from the second is transferred to
the first
oCross contamination
By exposing one item of evidence to another, evidence from the first is passed
to the second
Glass and napkin packaged together
oMechanical fit
When a damaged item leaves pieces at the scene, it may be possible to match
those pieces to the source object if located
Glass fragments from suspect fits glass from scene
Common Types of Evidence
oFingerprints
Fingerprints found at the scene provide individual characteristics which can
identify or eliminate a suspect by comparison to their known prints. No
fingerprints from different individuals have ever been found to match
Latent
Invisible; deposited by normal body secretions
