Dec 18, 2008

Bitemark Evidence Needs Orthodontia


Bitemark evidence is a tool that prosecutors sometimes use to connect defendants to crimes. The testimony of a bitemark expert (who carries the fancy, jury-impressing title of "forensic odontologist") usually goes something like this: "I compared the teethmarks found on the victim's right arm with the defendant's dental prints.  In my opinion, a match exists; the defendant was responsible for the teethmarks." 

Though judges routinely admit bitemark testimony, recent studies have undermined its reliability.  Unlike the generally-accepted principle that fingerprints are unique, the uniqueness of dental patterns has never been established. Moreover, bitemark experts usually have to base their conclusions on fragmentary patterns -- say, the marks left by a few teeth. Finally, the proficiency of bitemark experts is uncertain because they have never been scientifically studied.  Thus, it's no surprise that a number of defendants who have been cleared by DNA analysis after they have begun serving their sentences were convicted partly on the basis of mistaken bitemark evidence.

In the future, criminal defense attorneys will no doubt more aggressively challenge the admissibility of bitemark evidence. As "gatekeepers," judges have to remember that prosecutors who want to rely on bitemark evidence have the burden of establishing the reliability of its underlying principles.  If they cannot do so, judges should disregard the fancy trappings of forensic odontologists (advanced degrees, publications, professional associations, good molars) and tell them to bite the dust.