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Evidence-Based Crime Investigation. a Bayesian Approach

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Evidence-based Crime Investigation. A Bayesian Approach Ph.D. Elisabet Lund Department of statistical science University College London May 2012 Preface This dissertation is about evidence and inference in crime investigation. The question is: What can and should "evidence-based" crime investigation mean? My immediate aim is to contribute to the methodological toolbox of crime investiga- tion, but I also aspire to contribute to the concept and standard of evidence in real and public decision-making. Epistemology, methodology, and the foundational issues of different knowledge disciplines have been my basic intellectual interest since my student days. During the obligatory curriculum for a degree in political science at the University of Oslo, I gradually discovered that my talent, if any, was in methodology and analysis and not in politics. I did not have the maturity or boldness of my fellow much more politically minded students. While they rapidly formed an opinion on how things should be on almost any social or political matter I became stuck in the premises: How did they know that the premises of their opinions were sufficiently certain? Is not the certainty of the premises important if your opinion is to become actual policy, having real consequence to real people? I completed my degree in political science with a thesis analysing central foundational problems of political science (rationality vs. social norms; individualism vs. collectivism). Having "discovered" that the premises for these foundational conflicts were ideological too, the question became: By which criteria may we evaluate the knowledge-claims of public poli- cies? I wanted to pursue the concept and standard of evidence and justification in practical public decision-making. During my search for like-minded students, for funding, and for an interesting kind of problem, I read about the Norwegian Torgersen-case in the newspapers, a Norwegian crime-case from 1958 which could not find rest: Repeated motions for retrial were rejected, but the counsel of defence kept insisting that something was seriously wrong with the evidence-assessment in that case. A group of scientists joined in to add that something was seriously wrong with Norwegian legal evidence-assessment in general! I had found my problem: Few decision-problems are as acute, complex and consequential than legal decisions about the case-specific value of evidence in a given crime case. I contacted Staale Eskeland, professor at the Department of Public and International Law, University of Oslo, who had worked (and works) tirelessly to have the Torgersen-case reopened. He had carefully collected all the case-documents and did not hesitate to let me use them as sources in a PhD on legal assessment of evidence. He also offered to be one of my supervisors if the thesis was to be worked out in Norway. I am thoroughly grateful for his support and inspiration. Unfortunately no research-institution in Norway wanted to host what had to be an interdisciplinary Ph.D. Philip Dawid, professor in Statistics at the University College in London, had no such qualms: He was the Director of a research program specifically wanting cooperation across disciplines, Evidence, Inference and Enquiry. Towards an Integrate Science of Evidence (http://128.40.111.250/evidence/), and immediately invited me in. Joining this research program meant having to stay away from my family for long periods of time. But my wise husband (dear Arild!), knowing how much I wanted and needed to pursue my ideas, said I would be a fool not to accept the opportunity so generously offered by Philip Dawid. It was fortunate that I did not understand how much I was to miss my husband and children. It is impossible to thank Mathea, Marius, and Sandra, and my husband enough for letting me indulge in this rather selfish pursuit | I feel very lucky to have them. I am also very lucky to have my parents who always believe that I do the right things even when I do not (oh, you need to go to London to write the PhD? That is probably the best. Do you need money for that?). I thank them all I can for all the support through these years. The work with the thesis was far from straightforward. I do like to work and do like challenges, but I did at times feel overwhelmed. I simply did not understand how to make sense of the knowledge-situation in bitemark-analysis: While my fel- low students had access to reasonably clean data-sets, I had to start from scratch, making my own data from the information offered in pieces of natural prose. This was challenging but also very interesting | it was actually an opportunity to make sense of the cognitive process of natural as well as formal representing and modelling of reality. It unfortunately took a long time before I decided that the thesis had to be just as much an epistemological as a methodological study. Philip Dawid, my initial primary supervisor, may have wished for a more efficient student, but he never questioned the value of my work and ideas. My second supervisor, Dr. Christian Hennig came to be my primary supervisor when Philip Dawid left for a professorship in Cambridge. Christian Hennig is the incarnation of thorough- ness and precision, but fortunately also shared my curiosity about methodology. Despite my extraordinary degree of confusion Christian always took me seriously and carefully read and commented my presentations. I am very grateful that both Philip and Christian continued believing in this risky project: Thank you to both of you! 2 Contents 1 Introduction 11 1.1 A concept of evidence-basis relevant for crime investigative decisions. 21 1.1.1 Evidence-based decisions about the most relevant therapy for a given patient . 23 1.1.2 Evidence-based decisions about most likely diagnosis . 26 1.1.3 Evidence-based decisions about most likely diagnosis by expert- opinion alone . 30 1.2 Overview of the dissertation . 34 I The epistemological and institutional conditions of legal evidence and proof 41 2 The discourse on inference, proof, and evidence 43 2.1 Inference and justification | in the terms of epistemology . 43 2.1.1 Sensing and believing | a practical example . 46 2.1.2 What is an inferential belief? . 48 2.1.3 How may inference contribute to justification? . 49 2.2 Inference and justification | in the terms of jurisprudence and legal adjudication . 53 2.2.1 A brief history of legal theories of evidence . 54 2.2.2 Conclusion old scholarship . 57 3 The catalyst of the modern discourse on evidence and proof 59 3.1 The catalyst of the modern discourse on legal evidence and proof . 60 3.2 Probability: A suitable means towards sound practical arguments? 63 3.2.1 Three important premises . 64 3.2.2 Qualitative principles . 66 3.2.3 Quantification of degrees of belief and conse- quences . 68 3 3.3 Conclusion . 72 4 Formal approaches to evidence-assessments in legal adjudication? 75 4.1 Cullison (1969): A probability model of the trial process . 76 4.2 Tribe (1971) The case against formal approaches . 82 4.2.1 The case level: Formal approaches may cause loss of accuracy 83 4.2.2 The trial level: Formal approaches may cause loss of social values . 87 4.2.3 The procedural level: Formal approaches may cause loss to values sought via the procedural rules and norms of the legal institution . 88 4.2.4 Concluding remarks on Tribe (1971) . 89 4.3 A modern discourse on evidence and proof . 90 4.4 Conclusion . 93 II Determining the relevance of bitemark-means: Current epistemological norms and methodological procedures 95 5 The decision-problem exemplified: The Norwegian Torgersen- case 97 5.1 The Norwegian Torgersen case . 97 5.1.1 The crime investigation . 99 5.2 The court-history of the Torgersen-case . 100 5.2.1 The public prosecutor's indictment . 100 5.2.2 The trial and the court's decision in June 1958 . 102 5.2.3 A miscarriage of justice? . 103 5.2.4 The last effort: The Norwegian Criminal Cases Review Com- mission . 103 5.3 The relevance of the sources . 105 5.3.1 Excerpts to the High Court's Appeal's Committee, Crimi- nal Case Nr. 2000/1148, Fredrik Fasting Torgersen v. The Public Prosecution 2000; Volumes I-IV. 105 5.3.2 Eskeland (2005): The evidence in the Torgersen-case . 107 5.3.3 The Public Prosecution (2005): Statement to Fredrik Fast- ing Torgersen's Motion of 25. February 2004 for retrial of criminal case adjudicated by Eidsivating Court of Appeals 16. June 1958. 108 4 5.3.4 The Norwegian Criminal Case Review Commission (2006): Decision in case nr. 2004-00071, Fredrik Ludvig Fasting Torgersen v. The Public Prosecution Authority . 109 5.3.5 Are the sources sufficiently relevant? . 110 5.3.6 Independent decisions about the bitemark- means? . 112 6 The first decision about the bitemark-means in the Torgersen- case 121 6.1 The logical structure of the bitemark-means . 122 6.1.1 The logical consequences of PC and BM . 124 6.1.2 An inductive structure of the physical aspects of the bitemark- means . 128 6.2 Justifying the claim that BM was relevant to PC . 130 6.2.1 BM1 and BM4: "The suspect's biting- mechanism is the causal object of the bitemark?" . 131 6.2.2 "The bitemark on the victim occurred simultaneous with the lethal/rape injuries?" (BM2) . 140 6.2.3 Are the analytical norms and heuristics used in this case agreed to be conducive to the penultimate and ultimate purposes of the decision about the bitemark-proposition? (BM3) .
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