THE PRESIDENT’S COUNCIL of Advisors on Science and Technology has concluded that forensic bite-mark evidence is not scientifically valid and is unlikely ever to be validated, according to a draft report obtained by The Intercept. The report, titled “Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods,” is marked as a “predecisional” draft created August 26 that is not to be quoted or distributed, though the title page suggests the report will be made public sometime this month.
The report reviews a handful of common forensic practices, so called feature-comparison disciplines, or pattern-matching practices — bite-mark analysis, fingerprint and firearm analysis, shoe tread analysis, and DNA mixture analysis — each of which involves an “expert” looking at a piece of evidence and eyeballing whether it matches a particular image, person, or object. The report discusses whether each practice has been scientifically validated, what it would take to do so, and how each practice should be used in the courtroom — if at all.
In the case of bite-mark evidence, the report is especially critical. “PCAST finds that bitemark analysis does not meet the scientific standards for foundational validity, and is far from meeting such standards,” it reads. “To the contrary, available scientific evidence strongly suggests that examiners cannot consistently agree on whether an injury is a human bitemark and cannot identify the source of [a] bitemark with reasonable accuracy.”
Bite-mark analysis is conducted by forensic dentists and relies on two foundational premises: first, that human dentition is unique — as unique as DNA — and second, that human skin (or another malleable substrate) is a suitable medium on which to record such an impression. The problem is that neither premise has been proved. Nonetheless, bite-mark analysis has been used in criminal cases to match individuals to alleged bites since the 1950s, when Texas’s highest criminal court cleared the way for its use (in that case, a dentist claimed that a bite mark left in a piece of cheese found at the scene of a grocery burglary matched the teeth of a particular man).