Peter Barnett is a general criminalist with experience in the examination of physical evidence from a wide variety of incidents. Physical, chemical, and microscopical analysis is used in the examination of a variety of types of physical evidence, including impression evidence (such as fingerprints, shoe prints, and tool marks) and trace evidence (such as paint, hair, or fibers). These analyses can lead to the identification of perpetrators, association of one individual with another individual or a scene, or a more comprehensive understanding of the series of events that occurred during an incident under investigation.

Pair of Levi's ready to be processed for trace evidence.

Trace evidence is recovered from clothing using a variety of techniques, including removal of visible material and using sticky tape lifts to remove material not readily apparent. Examination of the material recovered from a victim's or a suspect's clothing may allow an association to be made between that individual and other people, places, or things that are involved in the investigation.

Photomicrograph of animal hair scales and root.

A common type of trace evidence recovered from clothing and bedding is animal hair. Animal hairs differ from human hairs in microscopic appearance so the type of animal from which the hair came may often be determined by examining the hairs under a microscope. Although individual animals cannot normally be identified, the finding of similar animal hair on two items recovered during an investigation may be circumstantial evidence that these two items were in contact with each other or with a common source of animal hair.

Blood spatter at the scene of an assault.

Blood spatter analysis involves the study of the distribution and pattern of blood stains at a crime scene. By understanding the effects of various types of physical forces on blood, and the interaction between blood and the surfaces on which it falls, it is often possible to determine the nature of the event that caused the blood spatter, the location of the person shedding the blood, the location and actions of an assailant, and the movement of the assailant or victim during the incident.