High Percentage of False Positives in Bite Mark Evidence
Forensic odontologists who analyze bite mark evidence rely on two foundational premises. The first is that human skin is a suitable medium to capture data from, which as we discussed in our last post, is not true due to the elasticity of the skin. The second premise is that human dentitions are unique. The theory behind uniqueness is that each individual person has a unique bite mark and that bite mark can be traced back to that specific person.
As stated in a 1984 paper, “human dentitions are unique beyond any reasonable doubt.” The paper discussed an experiment that studied 397 bitemarks that were made in wax wafers. Each bite mark was measured using 12 parameters. The scientists conducting the experiment assumed, without any evidence, that the parameters had no correlation whatsoever. By assuming that, the scientists were suggesting that two bite marks having the same parameters is less than one in six trillion. This paper was purely theoretical, not empirical, meaning the scientists did not actually compare the bite marks to one another.
The claims stated in the 1984 paper were later criticized and debunked in a paper published in 2010. The 2010 study looked at 344 dental casts and measured them by using a 3-D laser scanner. The study revealed that matches occurred much more often than the 1984 theoretical study claimed. In fact, the 2010 study revealed 32 matches when looking at a single five tooth dentition. Studies similar to the 1984 study have flooded the courts suggesting that bite mark analysis and bite mark testimony can produce reliable conclusions. However, according to the National Academy of Sciences Report, even with the guidelines and techniques that are in place, experts had a variety of results, and there was a high percentage of false positive matches of bite marks in controlled comparison studies.
Studies similar to the 1984 study set the foundation for how bite mark evidence would be used in the courtroom. Not only was it assumed that skin was a suitable medium to capture data from, it was also assumed that human dentitions are unique beyond any reasonable doubt. This made it appear that the use of bite mark evidence was valid and would be helpful. However, modern science has exposed the flaws found in the old science. Courts still allow bite mark evidence to be admitted into court which has resulted in numerous wrongful convictions on the basis of bite mark analysis. Both of the foundational premises that bite mark analyses were built off of have been largely criticized and debunked proving that the use of bite evidence should not be a valid practice allowed in the courtroom.
Erin Powers is a Law Clerk at Ambrose Law Firm, PLLC in Minneapolis, Minnesota. Erin is in her second year at the University of St. Thomas School of Law. She went to undergrad at the University of Minnesota where she graduated magna cum laude. She also volunteered for the Center for Integrity in Forensic Science. Criminal Defense Attorney Woodbury MN; Criminal Lawyer Minnesota; and Criminal Appeals Lawyer Minnesota.