Jury Perception of Bullet Matching Algorithms and Demonstrative Evidence

Subjective pattern comparison has been subject to increased scrutiny by the courts and by the general public, resulting in an increased interest in pattern comparison algorithms that provide quantitative assessments of similarity for use by forensic scientists. While these algorithms would mark an improvement over current subjective comparison methods, individuals without a statistical background may struggle with the statistical concepts and language necessary for describing algorithmic methods.

forensics
user experiment
Author

Rachel Rogers

Published

April 13, 2023

If algorithms are to be used, examiners must be able to testify about their use in a way that is accessible to the jury. We conduct a similar assessment of language and supporting visual aids which might be used to explain bullet matching algorithms. We use short, simulated, text-based transcripts of testimony, presented to jurors in an online environment. Scenarios manipulate the expert’s conclusion, the use of demonstrative evidence, and the use of a bullet matching algorithm by the forensic scientist. The only evidence linking the defendant to the crime was a recovered bullet in these scenarios. The algorithm evidence consists of a brief overview presented by the forensic scientist complete with a match score and interpretation corresponding to their own personal bullet comparison, as well as an algorithm expert explaining how bullet signatures are extracted and the algorithm uses a random forest to compute the match score. This process was modelled after testimony about DNA, which typically follows this format. Participants are asked to evaluate the credibility of the experts, the reliability of the methods, and the strength of the case against the defendant.