The logical foundations of forensic science: towards reliable knowledge

Abstract

The generation of observations is a technical process and the advances that have been made in forensic science techniques over the last 50 years have been staggering. But science is about reasoning —about making sense from observations. For the forensic scientist, this is the challenge of interpreting a pattern of observations within the context of a legal trial. Here too, there have been major advances over recent years and there is a broad consensus among serious thinkers, both scientific and legal, that the logical framework is furnished by Bayesian inference (Aitken et al. Fundamentals of Probability and Statistical Evidence in Criminal Proceedings ). This paper shows how the paradigm has matured, centred on the notion of the balanced scientist. Progress through the courts has not been always smooth and difficulties arising from recent judgments are discussed. Nevertheless, the future holds exciting prospects, in particular the opportunities for managing and calibrating the knowledge of the forensic scientists who assign the probabilities that are at the foundation of logical inference in the courtroom.

Evaluation of Forensic DNA Traces When Propositions of Interest Relate to Activities: Analysis and Discussion of Recurrent Concerns

“…Currently, results from empirical research are mainly published in peer reviewed scientific journals, but there is no systematically organized body of research. The idea of developing a knowledge base (Evett, 2015), to be shared among scientists who all contribute to the system, would thus represent a major contribution to strengthen the data-supported evaluations.…”

“…At trial, however, the requirements are different. At trial, the defendant has already been selected, and if DNA is to play any further role, it must be given a weight (Evett, 2015)—not against any propositions, but propositions at the relevant level.…”

“…It highlights the need for the elicitation of expert probabilities and knowledge through formal methods and techniques, known also in other areas of specialization, such as risk and safety assessments (e.g., O'Hagan et al, 2006; Aven and Reniers, 2013). There is merit in further developing these approaches for forensic science applications, as well as strengthening the body of structured knowledge (i.e., relevant data on phenomena such as transfer and persistence) for various types of forensic traces (Evett, 2015). This rejoins the idea of developing a knowledge base system that would include experiments and exemplar probabilistic models for evaluation (e.g., BNs).…”

Bayesian networks for the interpretation of biological evidence

“…An alternative approach, sourcing data from the literature is a possibility providing that the data can be found. The idea of systematically organizing data such as research into the transfer and persistence of different evidence types is not new (Biedermann et al, ; Buckleton & Walsh, ; Evett, ; Szkuta, Ballantyne, Kokshoorn, & van Oorschot, ), but centralized open source resources are still not readily available. Such a repository would allow greater sharing of knowledge as well as more consistency between scientists.…”

The Limits of Forensic Evidence

“…Rather, knowledge should be managed effectively through training and calibration. At a 2015 Royal Society discussion meeting, Evett put forward the argument that “the reliability of scientists' opinions should be judged, at least in part, by their performance under controlled conditions” 6 . In that way, he says, “when the expert goes to court, the expert doesn't say, ‘Believe me because I've been doing this job for 40 years’; they can present a documented set of studies in which they have participated, and this shows what their performance is like”.…”