The Goal: Preventing Contamination
Responsible investigation of a homicide starts with prompt response to the homicide crime scene by the police. Arriving patrol officers should immediately identify and protect the boundary of the crime scene, safeguarding evidence before it’s trampled under foot, moved, carelessly altered, contaminated or removed. Because the location of the body yields an abundance of physical evidence, everything must be considered evidence and every effort should be made to observe, note, catalogue, and preserve that evidence. Unfortunately, many police officers are poorly trained in protecting a crime scene and, as a consequence, valuable trace evidence is lost or destroyed.
Identifying the parameters of the crime scene can be difficult. There may, in fact, be multiple crime scenes for one homicide. The location of the body is normally regarded as the primary crime scene. Other crime scenes may include: (1) the location of the physical attack, if any; (2) the location of death; (3) the vehicle, if any, used to move the body; (4) the body and clothing of the victim; (5) the body and clothing of the accused; and, (6) the living quarters of the accused. Multiple crime scenes are possible because of the theory of transfer or exchange – which refers to the exchange between two objects that have come into contact with each other. A murderer may leave behind traces of himself at each scene (fingerprints, hair, skin, blood, plant matter, clothing fibers); he may carry away on his body or clothing traces of the victim or of a crime scene; and, the victim’s body may retain traces of the perpetrator or the scene where he was assaulted, where he died, or any vehicle within which he may have been moved.
The crime scene investigator retained by the criminal defense lawyer will very likely have to rely on the police reports slanted against the client, review low quality photographs, and examine physical evidence long after that evidence has been handled, stretched, cut, soiled, tested, and stored by crime laboratory personnel of varying experience. The ability of the defense attorney’s forensic investigator to discover the truth from the evidence can be compromised by the lack of ethics, competence, or accountability of the crime lab staff.