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Challenging bite mark evidence in courts

Watch Devina Malaviya and Shreya Rastogi explain how lawyers can challenge bite mark evidence in their case
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In this video, we will discuss how lawyers can examine and challenge the use of bite mark evidence in their case. The lessons have highlighted that the two assumptions on which bite mark comparison evidence is based are not scientifically supported. These
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assumptions are: First, that the human dentition, particularly the front teeth involved in biting, are unique to all individuals. Second, that the unique features of the teeth are recorded in the bite mark. Despite this, bite mark evidence has been used for conviction and sentencing in criminal cases in various jurisdictions. So, how did that happen? Historically, bite mark comparison has been used as a tool for investigation and subsequently as evidence in court. However, its underlying premise to link specific individuals to suspected bitemarks has been rigorously tested more recently, especially after the report of the National Academy of Sciences in the United States in 2009.
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This Report noted that there was no evidence of a scientific basis for identifying an individual to the exclusion of all others.Despite the lack of any scientific basis, experts have overstated the certainty of their results through various terms such as - match between the accused’s dentition and the suspected bite mark. The bite mark is “without a doubt inflicted by” the suspect. That there is a “one in a million” chance that someone other than the suspect bit the victim. Or there is “reasonable medical certainty” that the bite mark is caused by the accused.The judges and trier of fact accepted such evidence by experts believing it to be scientifically accurate.
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Once such evidence was accepted and relied on, courts generally looked at precedents while examining the evidence in their own case rather than scrutinising it from a scientific lens. However, research in bite mark comparison has revealed its lack of scientific validity. In 2016, a group of eminent scientists constituting the US President’s Council of Advisors on Science and Technology reviewed literature relating to seven forensic disciplines including bite marks. With respect to bite marks, the Report found that examiners cannot even consistently agree on whether a patterned injury is a human bite mark, let alone identifying its source. Based on review of such scientific studies, the PCAST Report concluded that the prospects of developing bitemark analysis into a scientifically valid method were low.
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They even advised against devoting significant resources to such efforts. Despite this, the law has been slow in keeping up with these changes. Challenging such evidence in Court may lead to resistance from the Bench. For decades, judges have reposed faith in expert forensic evidence due to the intuitive belief in the infallibility of science. This belief rests on the assumption that forensic disciplines such as bite mark analysis are indeed “scientific”. Even though there may be some resistance from the Bench, it is essential for lawyers to critically examine and challenge this belief. Not only is this important for your case, but it will also promote the use of scientifically reliable techniques in the legal system.
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So, how can a lawyer challenge bite mark evidence in their case?
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In a case involving bite mark evidence, the bite mark impression of the accused may be present on the victim, the victim’s bite marks may be found on the accused or such marks may be found on an object at the crime scene. In challenging such evidence, the first step is to ensure that you have access to all the relevant documents in the case. These include- Colour copies of the photographs of all the injuries including suspected bite marks on the victim. The scans of the dental models of the suspect and the laboratory documentation and notes of the odontologist. It is possible that these documents are not provided to you along with the bite mark report.
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In this scenario, you must file an application specifically seeking these materials in order to understand the process of bite mark comparison followed by the expert and whether it complies with the established protocols. Also, these materials will be important in case you wish to seek an opinion from an independent expert on the report. In the coming weeks, the lessons on expert evidence will deal with when and how lawyers can engage a defence expert. Now, for developing a strategy to challenge bite mark evidence in a particular case, two aspects must be considered.
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Firstly, to challenge the scientific validity and reliability of bite mark comparison as a forensic discipline and secondly, to challenge the manner in which the expert has carried out the bite mark comparison in your case. The argument on scientific validity of bite mark comparison may be explored as a challenge to the admissibility of such evidence.
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Since the evidence of a forensic odontologist is admitted as scientific evidence, the foundations of bite mark comparison must be considered by courts. You may submit arguments citing scientific studies and literature, that there is a lack of data to firstly, support the claim of uniqueness of human dentition. Secondly that distinctive features are recorded in the bite mark impression and thirdly, that these three-dimensional features can be reliably examined by an odontologist through two-dimensional photographs and compared to the suspected dentition. Further, if your case involves a suspected bite mark on skin, you may also submit scientific evidence on skin as a poor impression material Next, the technique followed by the odontologist in your case must also be challenged.
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For this, you must consider the following aspects. First, how was the evidence collected from the victim and the suspect? In case of a deceased victim, it is important to consider how the crime scene was managed, the handling of the deceased’s body, when the photographs were taken and whether they were taken before or after the post mortem procedures. Second, how have the injuries been photographed and whether the correct method was followed. Third, who prepared the dental casts of the suspect? This question is important because issues of bias can arise if the same odontologist collects the evidence from the suspects and thereafter examines it.
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Fourth, what are the qualifications of the person who conducted the bite mark analysis? Are they “specially skilled” in the area of forensic odontology and satisfy the criteria of an expert? Fifth, was a dental line-up of persons other than the suspects created in order to avoid issues of confirmation bias? Sixth, how was the bite mark examined? The expert must first examine the characteristics of the injury to determine if it is a bite mark and whether it is a human bite mark. If the expert is satisfied that the bite mark is of human origin, they must identify the individual characteristics visible from the bite mark and record their findings. This analysis must be done before it is compared to the suspect dentition.
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Seventh, what method was used in comparing the bite mark to the dentition? The expert report should clearly specify the method of analysis and comparison. Depending on the technique followed, it is important to consider the known error rates for such a method and submit it to court for consideration. Eighth, how have the conclusions been stated by the expert? The conclusions of the expert cannot be stated in terms of a definitive match, to indicate that it is to the exclusion of all other individuals. Remember, such a conclusion is scientifically inaccurate. And finally, has there been any independent verification of the results? As far as possible, the findings must be independently verified by another odontologist, before they are reported.

By now you have gained an understanding of the serious concerns surrounding the scientific validity and reliability of bite mark analysis. With this understanding, how can you apply these learnings to casework? In this video, Devina Malaviya and Shreya Rastogi from Project 39A discuss how lawyers can challenge bite mark evidence.

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Decoding Forensics for Legal Professionals

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