The primary function of the autopsy is to determine the cause, manner and mechanism of death. The manner of death in a forensic case is generally homicide or suicide, as opposed to natural causes. The cause of death could be from gunshot or knife-inflicted wounds, blunt force trauma, hanging, etc. The mechanism of death refers to the actual agent used, such as poison, baseball bat, gun, kitchen knife, etc. The autopsy can often provide much evidence about the size, shape and any unique features of the murder weapon. Time of death is also determined, as well as lividity the pooling and discoloration of blood in the lower extremities. Lividity is helpful in determining if a body has been moved from the crime scene to another location after death.
The term autopsy comes from the Greek "to see for oneself." The forensic pathologist first performs an overall examination of at the entire body. This includes the hair and fingernails, all bodily orifices, the skin for evidence or needle marks, all external wounds and burses. Evidence such as fibers are often entrapped in the victim's hair, so the hair is meticulously combed for any evidence. In rape cases, the pubic hair of the victim is examined for any evidence of semen or body fluids and for potential hair from the perpetrator. Gunshot entrance and exit wounds are thoroughly examined and probed to reveal bullets or bullet fragments. They are also probed to determine the potential position of the shooter in relation to the victim at the time of the shooting. Stabbing wounds are also probed for any evidence of the weapon and the pattern of the wound in the skin. Photography at all stages in the investigation is a critical part of the forensic autopsy.
Trace evidence is often collected from the body surface at autopsy. These might be hairs, fibers, small fragments of plastic, paint or glass that may have come from the murder weapon or the crime scene. Dirt or soil on the body or on the victim's clothing can provide a clue to where the victim was actually killed, if it os believed that the body was moved to a different location. Similar soil found on a potential suspect's shoes or the tires of his car can provide a link of the suspect to the victim and to a crime scene location.
The remainder of the autopsy involves opening the body and removing the organs, which are weighed and examined for any injury caused in the crime that may have contributed to the victim's death. The brain is removed and treated in a similar manner. If blunt force trauma is the cause of death, the damage to the skull and brain may provide clues to the nature of the murder weapon, especially if no weapon is readily apparent at the crime scene. Tissue samples and blood are removed and subjected to various laboratory procedures by the forensic laboratory. Routinely, a toxicology blood screen is run for drugs and poisons or other compounds that might be the cause of death. These samples may also be subjected to other procedures like microbiological or immunological tests as directed by the pathologist.
The forensic autopsy can determine with reasonable certainty how the victim died and estimate the time of death. However, it cannot determine where or why the victim died.
The autopsy finding becomes an integral part of the crime investigation and can in many instances guide investigators in the right direction in pursuit of the perpetrator.