As of early March 2023, the answer is clear—the problem with determining admissibility of bitemark comparison evidence is one of the law of Evidence, for the science is now beyond dispute and carries the imprimatur of the preeminent US government agency on science and measurements—The National Institute of Standards and Technology (NIST).
A bit of background is in order. The history of DNA exoneration shows, again and again, the errors in claims of bitemark “identification,” starting in and around 2000 in the cases of James O’Donnell, Ray Krone, Levon Brooks, and Kennedy Brewer and moving forward. [For a complete list, see Innocence Project, Description of Bite Mark Exonerations (updated Apr. 2020).] Yet the forensic odontologists soldiered on, claiming in various cases that the comparison was a “perfect match,” “one in a million,” “that of the biter,” and a match to a “reasonable dental certainty.”
The criticism grew as acceptance continued. The 2009 report Strengthening Forensic Science in the United States: A Path Forward noted that bitemark evidence “is introduced in criminal trials without any meaningful scientific validation, determination of error rates, or reliability testing.”
The repudiation continued. In 2015, an Obama administration science official called for the “eradication” of bitemark comparison testimony. Priscilla Ann Ornido, High-Ranking Obama Official Calls for Eradication of Bite Mark Evidence, Santa Clara Univ. (Aug. 11, 2015). In September 2016, the President’s Counsel of Advisors on Science and Technology issued its report on the state of various forensic disciplines and concluded the following:
Few empirical studies have been undertaken to study the ability of examiners to accurately identify the source of a bitemark. Among those studies that have been undertaken, the observed false positive rates were so high that the method is clearly scientifically unreliable at present. (Moreover, several of these studies employ inappropriate closed-set designs that are likely to underestimate the false-positive rate.)
Report to the President: Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods 87 (Sept. 2016). This conclusion came after a comprehensive review of all of the research addressing whether (1) dentition is unique and (2) forensic bitemark comparison had validity.
Now, NIST has weighed in. The March 2023 release of Bitemark Analysis: A NIST Scientific Foundation Review makes all these points (quoted verbatim):
•KEY TAKEAWAY #1.1: Forensic bitemark analysis lacks a sufficient scientific foundation because the three key premises of the field are not supported by the data. First, human anterior dental patterns have not been shown to be unique at the individual level. Second, those patterns are not accurately transferred to human skin consistently. Third, it has not been shown that defining characteristics of that pattern can be accurately analyzed to exclude or not exclude individuals as the source of a bitemark.
• KEY TAKEAWAY #2.1: The entire human dentition is not represented in a bitemark. Bitemark patterns typically only represent the anterior teeth and thus not the full possible dentition of an individual, limiting the amount of information available for an analysis.
• KEY TAKEAWAY #4.1: There is a lack of research into population frequencies, specific identifying characteristics, and measurements that support the notion that human anterior dental patterns as reflected in bitemarks are unique to individuals.
• KEY TAKEAWAY #4.2: Accurate transference of an anterior dentition pattern in the form of a bitemark on human skin can be limited by distortions caused by skin elasticity, unevenness of the biting surface, location of the bite, and movement of the biter and/or victim during the biting event.
• KEY TAKEAWAY #4.3: Comparisons between bitemark patterns made on skin, for example multiple bitemarks from the same individual on the same victim, have shown that there exists intra-individual variation in bitemark morphology on the human body such that bitemarks from the same biter may not appear consistent.
• KEY TAKEAWAY #4.4: Bitemarks in cadaver-based research studies are representative of highly controlled experimental conditions and these results may overestimate the accuracy of analysis methods. Bitemarks in actual cases, where controlled conditions are not present, are prone to higher levels of inaccuracy.
• KEY TAKEAWAY #4.5: As reflected in research studies to date, bitemark examiners may not agree on the interpretation of a specific bitemark, including whether the injury is a bitemark, the features present, and the exclusion or non-exclusion of potential biters.
• KEY TAKEAWAY #5.1: Repeated calls for additional data by critics and practitioners (since at least 1960) suggest insufficient support for the accurate use of bitemark analysis and a lack of consensus from the community on a way forward.
Kelly Sauerwein, John M. Butler, Karen K. Reczek & Christina Reed, Executive Summary in Bitemark Analysis: A NIST Scientific Foundation Review, NIST Interagency Report, NIST IR 8352 (2023).
The overarching finding? “[T]he ability of bitemark analysis to accurately exclude or not exclude individuals as a source of the mark is not supported.” Id.
Now, they’ve said it again. How can this possibly be “general acceptance” under Frye or “reliable” under Daubert? Put simply, it can’t. The time for bitemark comparison testimony should be over.