Bite Mark Analysis

The combination of a quick a thinking investigator, a skilled photographer and two highly credible expert witnesses made bite mark analysis pivotal in the conviction of a monster. Ted Bundy was not the first or the last to be convicted on analysis of a bite mark but he certainly was the most famous.

Collecting the evidence

One of the goals in any criminal investigation is to collect evidence which when analyzed will either confirm the involvement of a particular individual or exonerate them. In any investigation the investigators will formulate as many hypotheses as possible regarding the circumstances of the crime. The results of the evidence analysis will then be used to disqualify each hypothesis until one remains. If the evidence does not support the events of the final hypothesis the investigator then needs to develop a new hypothesis based on the evidence.

There are four main elements to an investigation (Millar, 2003) First, the crime scene is thoroughly documented. Photographs, videos, sketches and notes describing the scene are made. Second, the physical evidence is collected and unknown substances are sent to the laboratory for identification and analysis. Third, the results of the laboratory analysis of the physical evidence are compared to witness statements. Finally, both witness statements and laboratory results are used to disprove the investigator’s hypotheses until one remains.

Types of Evidence

Physical evidence can broken be down into two general categories. There are types of physical evidence which can be considered have “class” characteristics. Evidence with class characteristics can be said to have similar characteristics within a group but can not be linked to a particular individual. An example of evidence which has class characteristics is as blood types (Saferstein, 2004). All blood types exist in any given population. The blood type itself only indicates the percentage of people in a population from which the sample could have come from based on the ratio of occurrence in that population. It does not tell an investigator what particular individual the sample came from.

This is not to say that evidence with class characteristics is not useful. Several different kinds of evidence such as hair, blood type and glass fragments together may significantly raise the probability of linking a suspect or victim to a crime scene (Saferstein, 2004)( Crocker, 1999).

The second type of evidence is that which exhibits ‘individual’ characteristics. This type of evidence has numerous points of comparison. Each point of comparison from an ‘unknown source’ which matches a ‘known source’ sample raises the probability of the two samples having the same origin (Saferstein, 2004). In short, the huge number of comparison points in things like DNA samples or fingerprints makes it possible to match these types of samples to a particular individual with a very high probability. Some bite marks (as in the Bundy case) can be considered to have individual characteristics.

Evidence with class characteristics are best used to confirm the events of a crime (Saferstein.2004). Evidence with individual characteristics can identify an individual source.

Forensic Odontology (dentistry) has been used as far back as the Roman Empire to identify victims of crime and other mishaps. Bite mark analysis is somewhat newer but is gaining acceptance as a forensic tool. When the bite mark is not sufficiently deep to reveal the unique characteristics of each tooth it can only be said to have “class” characteristics. However, the location, size and number of wounds can be used as a useful indicator of the type of crime and possible group of suspects. Criminal profilers often analyze the position of wounds to develop a profile of the offender (Douglas, 1998)

In a non-sexually based assault bite marks may be found on the fingers, ears, nose, chest and thorax (Lane, 1992) In cases of sexual assault where the victim is female wounds tend to cluster around parts of the body associated with sexuality. Bite marks might be found on the neck, front of the shoulder, arm, breast, pubic area, buttocks and thigh (Lane, 1992). In a male victim bite marks might be found on the arm, chest and abdomen (Lane, 1992)

In cases of homosexual assault there is only data for male victims according to Lane (1992). In male victims bite marks might be found on the back of the shoulder, back, arm or armpit, chest, penis or scrotum (Lane, 1992).

In addition to the location of the bite mark the type of severity of the injury may give investigators clues as to the mental state of the offender. A hemorrhage is a blood spot. An abrasion is a bruise with out damage to the skin. A contusion is a broken blood vessel. A laceration is torn or punctured skin. An incision is a neat puncture of the skin. An avulsion is removal of the skin. Finally an artifact is where a piece of flesh or body part is completely removed (Genge, 2002) All of these categories indicate a level of violence. From this investigators can infer the mental state of the offender.

In cases where the bite mark causes sufficient damage to the flesh it is possible determine the unique characteristics of each tooth. It is then possible to match these unique characteristics to a particular individual (Saferstein, 2004) (Bowers, 2004). The size and shape of the wound will be affected by the place on the body where it occurs because certain areas of the body bend distorting the surface area of the skin (Bowers, 2004).

Some bite marks might only be represented as a bruise. In these cases it rare to be able to determine individual characteristics (Bowers, 2004) Dr. Bowers (2004) recommends that thorough analysis of the size, position and other features of bite marks be completed before any comparison with a suspect’s dentition is made.