Bite marks may be found at the scene of a crime and their analysis has been used for many years as an aid in forensic investigation. Bite marks can occur on the skin of a victim or on other objects, including foods such as cheese, chocolate, or apples. Non-food items that may bear bite marks and are therefore worthy of investigation include chewing gum, bottle tops, masking tape, and pencils. The bite mark itself may be matched to the bite mark of a suspect. There is also the possibility of gathering saliva from the bite mark, which can then be used to identify a suspect through DNA analysis.
Bite marks tend to have a double horseshoe pattern showing the six central teeth of the upper jaw and the corresponding six teeth in the lower jaw. Those made in food are usually well defined; bite marks made in flesh are usually less defined. The analysis of a bite mark begins with photographing the evidence in both black and white and in color, and from several angles. It is important to take these photographs within eight hours of the injury being inflicted in the case of a victim. Inflammation tends to blur the pattern after this time if the victim is alive. If the mark is deep enough, then a cast can be made using dental processes similar to those used for making a tooth crown or a bridge. The next step is to make an image that can be overlaid on the bite mark of a suspect for comparison. The image can be made by manual tracing or by scanning into a computer and using a program that makes a picture on a transparent overlay sheet.
Bite marks reveal features such as gaps between the teeth, ridges on the biting surfaces of the teeth, rough fillings, as well as missing, broken, chipped, or distorted teeth. In fact, human teeth patterns are individual and careful expert analysis of a bite should be able to tie the mark to a suspect. Identification through bite mark analysis is given over to a forensic odontologist, who is a specialist in dental anatomy and its interpretation.
Flesh is elastic and stretches when it is bitten. A bite mark on a body, therefore, is somewhat different from a bite mark on an inanimate surface. A forensic pathologist will note a bruising pattern in the shape of two curved lines facing one another if the bite has been inflicted antemortem (before death). Bites inflicted on muscular tissue make a more distinct pattern than bites found on fatty tissue. Postmortem bites do not produce bruising. Particularly ferocious bites will produce lacerations. Bite marks on a victim tend to be specific to the nature of the attack. For example, bite marks on the neck, breasts, and shoulders are seen in some rapes, sexual assaults, or incidents of domestic violence. Multiple bites on the arms or buttocks are sometimes a feature of child abuse. Sometimes a victim may bite the suspect as a means of the defense using the teeth as a weapon; this tends to produce multiple bites, rather than single bites.
It is also important to take sterile swabs of the bite to collect traces of saliva. The presence of the enzyme amylase in the swab shows that saliva is present and the injury is indeed a bite. Microbiological evidence from the swab can also be informative if it corresponds to the microbial flora (microorganisms present) from the mouth of a suspect. It may also be possible to determine the blood group of the suspect from saliva analysis. This kind of evidence is useful for excluding a suspect, taken with the bite pattern analysis. If DNA can be extracted from the saliva as well, then the bite mark evidence for or against the suspect becomes even stronger.
One of the most famous cases involving bite analysis is that of serial murderer Ted Bundy. In 1978, a brutal attack at the Chi Omega sorority house at Florida State University left two young women dead and two others seriously injured. A fifth woman, who escaped, was able to describe her attacker. Bundy, an escaped prisoner, was caught and put on trial for the Chi Omega murders. A crucial piece of evidence for the prosecution was an enlarged photograph of a bite mark found on the left buttock of one of the victims. An image of the outline of Bundy's front teeth was created on a transparent overlay. Bundy's teeth were misaligned and chipped. According to the forensic odontologist, this matched perfectly with the photograph of the bite mark found at the scene. This helped identify Bundy as the attacker and he was found guilty and executed in 1989. Bundy confessed to up to 50 other murders.
see also Body marks; Bundy (serial murderer) case; Odontology.