Reasoning about Forensic Science Evidence
Forensic evidence has become a common tool in police investigations and a familiar form of evidence at trial. Forensic scientists are trained to analyze such evidence (e.g., fingerprints, handwriting, seized drugs, blood spatter, fire debris) and to provide reports and testimony concerning their findings. Despite the prevalence and potential usefulness of this type of information, there is widespread misunderstanding of how accurate and determinative forensic evidence can be. Lawyers and judges often do not have a good understanding of forensic science and its limitations even though they may need to make use of and critique forensic analysts and forensic evidence in the course of their work. This chapter first addresses how and when flawed reasoning, biases, and non-optimal laboratory conditions may affect forensic analysts and their conclusions. Then it describes what people—forensic experts, lawyers, judges, and jury-eligible lay persons—believe about forensic science. Finally, it explains strategies for how lawyers or judges can evaluate and communicate the value of forensic science evidence during trials, such that the ultimate factfinders will understand the evidence, what it means, and how to consider that evidence appropriately in the context of a particular case.