Criminal InvestigationsOConnor The Significance of Physical Evidence Forensic Science is unable to assign an exact or even approximate probability values to the comparison of most class physical evidence ID: 337051
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Chapter 3 Continued
Criminal Investigations/O’ConnorSlide2
The Significance of Physical Evidence
Forensic Science is unable to assign an exact or even approximate probability values to the comparison of most class physical evidence.
As more things in our world are mass produced, this becomes harder and harder. Slide3
Occasionally statistical data is available for use; like population frequency of blood factors.
More often forensic scientists must rely on personal experience when interpreting the significance of class physical data Slide4
Most items of physical evidence retrieved at a crime scene cannot be linked definitively to a single person or object.
Investigators try to find evidence with individual characteristics, like fingerprints- the chances of finding such evidence is much lower than finding class evidence. Slide5
Criminal cases are built for the courtroom around a collection of diverse elements, each pointing to the guilt or involvement of a party in a criminal act. Often, most of the evidence gathered is subjective, prone to human error & bias. The believability of eyewitness accounts, confessions, & informant testimony can all be disputed, maligned, & subjected to severe attack & skepticism in the courtroom. In such cases errors in human judgement are often magnified to detract from the credibility of the witness.Slide6
Assessing the Value of Evidence
Defining the significance of an item of class evidence in exact mathematical terms is usually a difficult if not impossible goal. As the number of different objects linking an individual to a crime increases, the probability of involvement increases dramatically.Slide7
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.Slide8
Forensic Databases
Computer technology has dramatically altered the role of the crime laboratory in the investigative process.
The creation of computerized databases that not only link all fifty states, but tie together police agencies throughout the world.Slide9
Fingerprint Databases
Integrated Automated Fingerprint Identification System (IAFIS) ~ maintained by the FBI since 1999.
Nearly 50 million subjects, which are submitted voluntarily to the FBI.Slide10
DNA Databases
Combined DNA Index System (CODIS)
CODIS creates investigative leads from two sources:
~The forensic index-110,000 profiles of unsolved crime-scene evidence.
&
~The offender index- 3 million convicted or arrested individuals.Slide11
Other Databases
National Integrated Ballistics Information Network (NIBIN)
International Forensic Automotive Paint Data Query (PDQ)Slide12
Crime-Scene 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.Slide13
Crime-scene reconstruction relies on the combined efforts of medical examiners, criminalistics, and law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crimeSlide14
Examples of crime scene reconstruction include determining whether a body was moved after death, determining whether a victim was clothed after death, analyzing bullet trajectory, analyzing blood spatter, determining the direction from which projectiles penetrated glass objects, estimating the distance of a shooter from a target, and locating primer residue on suspects.