Assessing the use of DNA expert evidence, by justice system participants, in Ontario criminal courts

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What happens to forensic DNA opinion evidence when the expert witness is not present in the courtroom? Research addressing this issue has largely been focused on polling lawyers regarding their perceptions of DNA evidence, as well as studies of juror understanding of DNA expert evidence in real and mock court situations. This thesis attempted to address the question in a different way, by analyzing transcripts of expert DNA evidence, opening & closing addresses, and judges’ instructions to juries, for cases that have passed through the Ontario criminal courts within the past fifteen years. This project is the first assessment of Canadian criminal court case transcripts, comparing expert DNA evidence with the (largely) non-scientist attorneys’ and judges’ inferred understanding and use of that evidence. Trial transcripts from cases involving DNA expert evidence were located by keyword searching Ontario Court of Appeal decisions via the Canadian Legal Information Institute (CanLii) public online database. This research question was approached from a social science methodology, making use of both qualitative and quantitative analyses. Quantitative analysis was conceptualized first, as a survey that was developed to track topics of interest in Interval Ratio and Nominal variable form. Qualitative Data Analysis (QDA) Miner 4 Lite™ was used to code sections of these transcripts and complete the survey. Coded sections involved random match probabilities (RMPs), likelihood ratios (LR), mitochondrial & Y-STR lineage confidence intervals, as well as body fluid attribution statements by attorneys and judges. These transcript excerpts were compared to each case’s respective DNA expert testimony. This enabled the application of qualitative analysis of question and response exposition within the expert testimonies. The survey data were inputted into IBM Statistical Package for the Social Sciences (SPSS) Statistics 24 for pattern analysis and descriptive statistics. For example, the sets of cases studied (N=32), contained 101 autosomal random match probability statements provided by DNA experts. Many times these RMPs did not enter into the crown summations (only 48.5%), defence summations (only 31.7%) or judges’ instructions (only 57.4%). When attorneys and judges did discuss and review the DNA statistical evidence, mistakes and misstatements occurred in the majority of instances – these mistakes included statistical fallacies and numerical misstatements. This research suggests a lacunae of knowledge with respect to the meaning of DNA evidence, and in particular, the correct understanding and communication of the RMP estimate of statistical weight of DNA profile comparison evidence. Further research is recommended, to address the use of transfer and persistence expert testimony, as well as testimony regarding complex mixture profile interpretations and comparisons
DNA, Random match probability, Transcript, Expert testimony, Justice system