Forensics Chapter 3

Physical Evidence
Requirements of physical evidence
recognized as potential evidence, collected in an appropriate manner, preserved properly for transmittal to laboratory
ex. blood, semen, saliva. must be present in a form suggesting a relation to the crime
the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit
Identification requirements
testing procedures that give characteristic results, repeatability, specificity,
Comparison analysis
subjects a suspect specimen and a standard/reference specimen to the same tests and examinations for the ultimate purpose of determining whether or not they have a common origin
Evidential value
the worth of the physical evidence in a court of law, relies on probability
Individual Characteristics
evidence that can be associated to a common source with an extremely high degree of probability (ex- fingerprints, DNA)
Class Characteristics
when it can be associated only with a group and never with a single source, narrows an identity to a group of persons or things
Product Rule
used to get a probability for comparison analysis
Probative value
the value of physical evidence in proving or disproving the hypothesis
Uses of physical evidence
establish a link according to Locard's Exchange Principle, provide investigative leads, provide visible facts to jury, reconstruction of the crime scene
Linkage Triangle
Victim, Suspect, Scene
Persistence of transfer evidence depends on:
nature of evidence, location of evidence, environment around evidence, time from transfer to collection, "activity" of or around the evidence location
national fingerprint and criminal history system
IAFIS (Integrated Automated Fingerprint Identification System)
enabled federal, state, and local crime laboratories to electronically exchange and compare DNA profiles
Combined DNA Index System (CODIS)
crime scene reconstruction
the method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident