Author:Chin, Jason M.

    [The President's Council of Advisors on Science and Technology] finds that bitemark analysis does not meet the scientific standards for foundational validity, and is far from meeting such standards. 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. (1) The forensic sciences are widely depicted as being precise and rigorous, (2) a portrayal that often diverges from their true epistemic status. (3) Indeed, recent reports from leading scientific bodies have found that several forensic scientific fields were never adequately tested and demonstrate unacceptably high error rates. (4) Forensic bitemark analysis is a prime offender in this respect. In 2016, a report from the President's Council of Advisors on Science and Technology (the "PCAST Report") provided the above quote. It built upon findings from a 2009 report of a committee of the National Academy of Sciences (the "NAS Report") that issued similar (but less insistent) warnings against using bitemark identification as inculpatory evidence in court. (5) Despite the clear prejudice such evidence presents to the criminally accused, there has been no systematic study of its use in Canadian courts. (6) In this article, we endeavor to fill that cavity.

    The (mis)use of bitemark analysis has been well-documented in the United States. (7) There, the practice has been implicated in at least 14 DNA-supported exonerations of wrongfully convicted individuals. (8) Less is known about the experience in Canada--both with respect to the use of forensic bitemark analysis specifically (9) and the forensic sciences more broadly. (10) Bitemark analysis provides a useful starting point for this broader inquiry because it is a discipline that has received some of the most piercing scientific criticism. For instance, while the PCAST Report suggested that various other forensic disciplines could improve, it was the least optimistic--indeed, fatalistic--when it came to bitemark analysis: "... PCAST considers the prospects of developing bitemark analysis into a scientifically valid method to be low. We advise against devoting significant resources to such efforts." (11) If there is any modern forensic field that courts should be on notice about, it is bitemark identification.

    To address these issues with the forensic sciences, both the PCAST and NAS reports recommended that these sciences and their regulatory bodies receive greater funding to strengthen their practices. (12) In early 2017, however, the subsequent American administration decided to defund such programs. (13) As a result, it has never been more important for the judiciary to understand the limits of the current forensic practices. Canadian courts and organizations can be expected to play a vital role in these endeavors in the coming years.

    In light of these scientific revelations and political transitions, it is important to know how Canadian courts are using bitemark analysis, how extensive that use is, and if that use is at all sensitive to the severe limitations of the practice. Although most scholars are profoundly pessimistic about the impact that legal standards have on admissibility decisions, (14) there may be reason to believe bitemark analysis is less problematic in Canada. For instance, Canadian expert witnesses may be more cautious in their opinions or defence counsel more skilled at rebutting such evidence. (15) Moreover, the Canadian justice system boasts a long and respected history of commissioning public inquiries in response to its failures. (16) Two of these inquires focused especially on failures of forensic science. (17) It is possible that these have had some impact on the use of bitemark analysis. Finally, uncovering just a few Canadian decisions that are critical of bitemark analysis would be useful to accused who may be confronted with such evidence. Indeed, courts generally seem to be more likely to follow precedent than embark on any form of scientific inquiry. (18)

    In what follows, we will present our review and analysis of the use of forensic bitemark identification evidence in Canadian courts. In Part II, we will briefly discuss the putative scientific foundation of bitemark identification. Then, in Part III, we turn to the law of expert evidence in Canada. We then build on that context to fulfil two aims: Part IV's comprehensive review of the published Canadian case law on forensic bitemark evidence and Part V's critical examination of those decisions. Part VI concludes with our recommendations for reform that are based around the principle of transparency.


    Before discussing the Canadian jurisprudence, a brief primer on the highly contested practice of forensic bitemark identification is useful in setting the scene. In this part, we first describe what it is that practitioners of forensic bitemark analysis (that is, forensic odontologists) do, (19) and why their task is so challenging. We then go on to summarize the research that has sought to measure the validity of forensic bitemark identification. This review will be brief because, as discussed above, the NAS and PCAST Reports recently provided thorough accountings of forensic bitemark analysis. (20) Moreover, shortly before the PCAST Report was published, Michael Saks and several other leading scientists and legal scholars published an overview of bitemark analysis and its impact on U.S. courts. (21)

    Along with techniques like DNA and fingerprint analysis, forensic bitemark analysis falls under a class of forensic methods that rely on feature-comparison. (22) Using such methods, analysts compare an evidentiary sample, such as one found at a crime scene, to a known sample, such as one taken from a suspect. Their goal is to determine if the two samples came from the same source. (23) Forensic odontologists compare a bitemark, often found on skin, to a known set of dental impressions. Much of this comparison is based on the arrangement of the front teeth, which are those that are typically engaged in the bites found in criminal investigations. (24)

    Matching a bitemark found on human skin to a suspect's dentition is a very difficult task. The found bitemark itself is almost invariably incomplete and of a poor quality. (25) While adults typically have 32 teeth, only the edges of the front teeth are involved in biting. (26) Further, skin (that is, the substrate) is not a good medium on which to create accurate impressions: "bite marks on the skin will change over time and can be distorted by the elasticity of the skin, the unevenness of the surface bite, and swelling and healing." (27) Indeed, a systematic research program using bitemarks made on human cadavers has found substantial variation in those bitemarks. (28)

    Another complicating factor is the lack of a standardized and rigorous methodology. For instance, there is currently no standardized criteria for determining whether the bitemark and dentition are sufficiently similar. (29) On this topic, the NAS Report concluded: "there is still no general agreement among practicing forensic odontologists about the national or international standards for comparison." (30) Further, "blinding", or keeping the analyst unaware of whether the sample is from a suspect or not, is not common in practice. (31)

    This flexibility granted to practitioners in how they come to their decisions opens the door for cognitive bias. (32) One form of such bias is "contextual bias", which occurs when irrelevant information about the case unconsciously affects the forensic scientist's judgment. (33) The current practice of forensic odontology provides a perfect storm of conditions for such bias--examiners have wide discretion in their decision-making and are often aware of the identity of the suspect. (34) Heightening these concerns is the reality that bitemark cases typically arise in very serious assaults (indeed, murders and sexual assaults were the subject matter of 9 of the 14 cases we reviewed, see Part IV). (35) In such cases, the desire to identify and punish the culprit is quite high.

    Even if forensic odontologists were appropriately blinded and their approach was more systematic and defined, their conclusions would be undermined by the fact that "[n]o thorough study has been conducted of large populations to establish the uniqueness of bite marks." (36) In other words, there may be many others--those who could have been the actual biter--with visibly identical dentition as the suspect. Without such data, it is impossible to say how often one would expect two bitemarks to appear identical by chance alone.

    In light of the serious challenges inherent in the bitemark analysis process, both the PCAST Report and the NAS Report concluded that bitemark analysis was not a demonstrably valid science. Furthermore, the PCAST Report stated that bitemark analysis was unlikely to ever develop into a valid science. (37) In the remainder of this part, we will review the existing failed attempts at establishing the field's validity.

    Scientific validity can be parsed into two components: foundational validity and applied validity. (38) Foundational validity focuses on the methodology, asking if it produces accurate results: does the conclusion that a bitemark matches a set of dental impressions accord with the "ground truth"? (39) In other words, when the method reports an identification, are the two samples actually from the same individual? Foundational validity also requires reliability: does the method consistently lead to the same results across both time and the forensic odontologist applying the method? Once it is determined that a method is foundationally valid, applied validity must be assessed. (40) Applied validity requires that the specific forensic odontologist be capable...

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