More than 3,750,000 pageviews from 150 countries


Thursday, July 27, 2017

Bite Mark Identification: A Forensic Science That Lost Its Credibility

     The identification of a series of bruises or abrasions, usually in the shape of two semi-circles or brackets, as a human bite mark made by a particular set of teeth is a function of forensic dentistry referred to a bite mark identification. This form of impression identification, also called forensic odontology, is based on the assumption that no two people in the world have front teeth that are identical in thickness, shape, relationship to each other, and patterns of wear.

     The process of comparing a bite mark to a known set of teeth is not unlike the identification of latent fingerprints, footwear, and tire track impressions. Bite mark wounds are found on victims of murder, rape, and child molestation. This type of crime scene evidence is preserved by life-size photography, tooth mark tracings onto transparent sheets, and dental casts of the impressions themselves. A suspect might be asked to bite down on a pliable surface for an impression sample, have a cast made of his teeth, or both. Usually, connecting a suspect to a victim through expert bite mark testimony will be enough evidence, by itself, to sustain a criminal conviction.

     The field of bite mark identification exploded in the 1980s, and hundreds, if not thousands of defendants between 1983 and 2002 were sent to prison on the strength of bite mark testimony. Although bite mark identification had been a recognized branch of forensic science since 1970, it was the 1979 trial of serial killer Ted Bundy in south Florida that put this form of identification on the map the way the O. J. Simpson case, in the mid-1990s, popularized DNA profiling.

     At the peak of bite mark evidence credibility among forensic scientists, detectives, prosecutors, and judges, this form of impression identification was put on the level with the matching of fingerprints. However, by 2003, forensic scientists were seriously questioning the assumption that bite marks were as unique and identifiable as latent fingerprints.

     Over the years several leaders in the bite mark field oversold the reliability of this form of identification. For example, in 1977, Dr. Lowell J. Levine, a forensic dentistry consultant to the New York City Medical Examiner's Office, wrote: "Since every person's teeth are unique in respect to spacing, twisting, turning, shapes, tipping toward the tongue or lips, wear patterns, breakage, fillings, caps, loss and the like, all of which occur in limitless combinations, it is possible for them to leave a pattern which for identification purposes is as good as a fingerprint."

     In 1996, Dr. C. Michael Bowers, a prominent southern California odontologist, was one of the first forensic scientists to raise doubts about the credibility of bite make identification when he wrote: "Physical matching of bite marks is a non-science which was developed with little testing and no published error rate....An opinion is worth nothing unless the supportive data is clearly describable and can be demonstrated in court. How does one weight the importance of a single rotated tooth in a bite mark when the suspect has a similar tooth? The value judgments range widely on the value of this feature. This is not science. Instead, statistical levels of confidence must be included in the process."

     In a bite mark identification exercise Dr. Bowers conducted in a workshop at the 1999 American Academy of Forensic Science conference, 63 percent of the odontologists who participated made an incorrect identification, findings that displeased many in the field when Dr. Bowers published the results of his experiment. In an article published in 2003 in the British Dental Journal, Dr. D. K. Whittaker, a forensic dentistry professor at the University of Wales, explained why bite mark evidence is so difficult to identify, particularly bite marks on skin:

     "Human bites on skin are difficult to interpret because skin is not good 'impression' material. Moreover, victims may struggle and movement will distort the image of the bite. Skin surfaces are not flat and visual distortion may be present, often heightened by photographic distortion caused by inadequate imaging techniques. Human dentitions, whilst possibly being unique in the small nuances of tooth size, shape, angulation and texture may not inflict unique bite marks which can only record gross and not fine detail. If the victim survives, the injury may change due to infection or subsequent healing and if the victim is deceased, putrefaction may introduce distortion."

     Before odontologists in Great Britain can testify in court as bite mark experts, they must have made a minimum of twenty such identifications in other cases. In the United States, an odontologist can be certified by the American Board of Forensic Odontology after two bite mark identifications. As a result, being certified in this forensic field in the United States shouldn't carry much weight. (In fact, two of America's most notorious charlatans in the field were both board certified bite mark experts.)

     In 2004, as part of a journalistic series on forensic science, the Chicago Tribune examined 154 state and federal trials involving bite mark identification testimony. In more than a quarter of these cases the prosecution and the defense produced forensic odontologists whose expert opinions were diametrically opposed. If bite mark identification is an exact science practiced by highly qualified experts, this many odontologists should not have been testifying against each other.


No comments:

Post a Comment