Chapter 3 Continued Criminal Investigations/O’Connor

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. 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. As more things in our world are mass produced, this becomes harder and harder.

Occasionally statistical data is available for use; like population frequency of blood factors. 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 More often forensic scientists must rely on personal experience when interpreting the significance of class physical data

Most items of physical evidence retrieved at a crime scene cannot be linked definitively to a single person or object. 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. Investigators try to find evidence with individual characteristics, like fingerprints- the chances of finding such evidence is much lower than finding class evidence.

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. 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.

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. 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.

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. 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.

Forensic Databases Computer technology has dramatically altered the role of the crime laboratory in the investigative process. 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. The creation of computerized databases that not only link all fifty states, but tie together police agencies throughout the world.

Fingerprint Databases Integrated Automated Fingerprint Identification System (IAFIS) ~ maintained by the FBI since Integrated Automated Fingerprint Identification System (IAFIS) ~ maintained by the FBI since Nearly 50 million subjects, which are submitted voluntarily to the FBI. Nearly 50 million subjects, which are submitted voluntarily to the FBI.

DNA Databases Combined DNA Index System (CODIS) Combined DNA Index System (CODIS) CODIS creates investigative leads from two sources: 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.

Other Databases National Integrated Ballistics Information Network (NIBIN) National Integrated Ballistics Information Network (NIBIN) International Forensic Automotive Paint Data Query (PDQ) International Forensic Automotive Paint Data Query (PDQ)

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. 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.

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 crime 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 crime

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. 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.