Marks left behind by teeth (bite marks) at crime scenes are notable for two intriguing reasons: they constitute valuable forensic evidence, which is brilliant from our perspective as crime analysts; but are also regarded as an indication of a particularly vicious crime.
Bite mark analysis has come a tremendously long way over the past few decades and has been used to convict some notable criminals (Ted Bundy, anyone?) As evidence, they’re particularly useful because teeth develop and wear into such a unique pattern, they become like a fingerprint – and are therefore almost impossible to attribute to any other individual than the suspect.
Patterns in the past: the short history of bite marks
Bite mark testimony has been used in Scotland since 1967. It began with the unfortunate and tragic case of Linda Peacock, a fifteen-year-old girl who went missing from her home. Eventually, her body was found in a local cemetery, replete with jagged bite marks. Investigators obtained bite mark impressions from individuals in a local detention centre and those made by the suspect – Gordon Hay. Hay’s teeth marks were believed to be so distinctive, it was almost impossible to attribute them to anyone else. Still, due to the untested nature of bite mark comparison at the time, the odontologist in the case profiled over three hundred other people to make sure his theory stacked up. Although it was the subject of heavy dispute in court, the bite mark evidence stood up to scrutiny and not only assisted in securing the conviction, but became admissible evidence from this point forward.
Making the mark: obtaining and studying bite patterns
Just how is bite make evidence collected and obtained? Well, clearly we require a victim with a bite mark, or a mark in another surface (perhaps a recently tossed apple core, or some such food item). The mark is photographed from several angles; with particular attention being paid to the angle at which the mark is believed to have been inflicted. The specimen must be well-lit and rulers measuring the width and height of the mark are placed in the photos for comparison (as well as control shots being taken without any measurements). In previous cases, these images were hand traced and superimposed over photographs of the jaw of the accused (see Ted Bundy), but computer technology has now taken over in this field, and has lead to much more accurate comparison.
After photography, if the mark is deep enough, an impression can be lifted. The area can then be swabbed to pick up any trace saliva or DNA that the suspect may have left behind. A further control sample swab is taken from elsewhere on the victim.
If and when a suspect is identified, an impression of their teeth is then made. In the UK, this comes under a class of samples known as intimate samples and is governed by the Police and Criminal Evidence Act. These samples cannot be taken without consent (the suspect cannot be forced to provide them), but should the suspect refuse to provide them an adverse inference can be drawn at court for this refusal. The suspect’s teeth are also rigorously photographed, to permit their reproduction, for compassion to the marks taken from the victim, at a 1:1 scale. As you might imagine, this process is fairly involved and technical.
Manipulating molars: altering a profile
Strangely enough, the astute investigator must also counter the possibility that the suspect may have altered the profile of his teeth in some way: by filing or grinding, removal or even through surgery. Therefore, part of the investigative process will involve following the trail of dental records as far as possible. However, even with crude techniques to wilfully alter their profile, it is extremely difficult to change the physical characteristics of the teeth enough to fool a forensic odontologist.
The process of comparing the bite mark made with dental impressions from suspect is, however, a far from certain assertion and open to interpretation. To prevent this, investigators will often use a double blind comparison to ensure that there can be no accusations of bias. Some bite marks, such as defensive bites are very difficult to identify. Criminal profiling can assist in identifying marks to a certain extent, but the presence of a bite mark alone at a crime scene is a far cry from having the case effectively nailed shut.
Even with all the above, bite mark interpretation is still subjective. There are cases of false conviction indicating how spurious the evidence can often be and demonstrates that confusion still surrounds the area. The American case of Ricky Amolsch shows how bite mark evidence can be misused, and even ignored in some cases.
Your Turn: Do you think that bite mark evidence should still be admissible, even if there are certain cases in which it wasn’t accurate? Believe that it’s up to the jury to decide which bite marks ought to be tossed out? Just fascinated by how marks can be utilised in CSI? Let us know in the comments. We’d like to hear from you.