Stories about Evidence

Floris Bex and Bart Verheij

Crime stories seem to come in an unbounded variation. This is evident from fictional crime stories and real crimes alike. In fiction, crime stories have been popular since at least Victorian times – with Sherlock Holmes and Jack the Ripper as prototypes of the rational good and the emotional bad – and remain to be adapted to a contemporary perspective as in the bleak Scandinavian crime series filled with social criticism. Actual criminals also keep surprising the public and the experts.

The variation of crime stories does not make the life of investigators easy. If only all criminals would nicely fit a few prototypes, say a typical drug gang-related drive-by shooting or hotel room crime passionel, it would be easy to determine what evidence can show what has happened and solve a case. In practice, it is often hard to determine what exactly happened in a crime, and – even if there is a strong hypothesis of who did it and how – it can be hard to uncover proof beyond a reasonable doubt.

A key issue is then how to rationally manage the evidence and hypotheses about what has happened in a crime in such a way that it can be determined whether the belief in a hypothesis is justified or not. When should we believe the prosecutor’s story of what has happened, and when has the defence raised a reasonable doubt?

To us it came as a surprise that stories play an important role in the rational analysis of evidential reasoning. We came to this conviction through our meeting with Peter van Koppen – grand reciter of crime stories and expositor of whether to believe them or not. For one of us (Bart), the exchange started in Maastricht when Peter was appointed as professor of legal psychology in the Department of Metajuridica (from 2003 to 2014). But the importance of stories only imbued our understanding of evidence when Peter joined Floris’ PhD research project as a supervisor (with Henry Prakken and Bart; from 2005 to 2009). It was in those days that Peter explained to us that we did not understand evidence at all. Evidence is all about stories, and only stories; such was his message. It took us a while to get a feeling for what he meant, and to appreciate the force of Peter’s message. Peters emphasis on open discussion ‘with our legs on the table’ as a scientific method helped us make progress and enjoy the erratic journey that is research.

In fact, we have come to the conviction that stories play a role that is only addressed by stories: guarding the local and global coherence of the events in light of the evidence. This role is neglected by the other two main rationality tools for evidential reasoning: arguments (focusing on managing conflicting information) and probabilities (analyzing evidential strength).

In the following, we discuss three parts of our journey with Peter, his stories about evidence and his perspective on artificial intelligence.

Manuscript (in PDF-format)

Chapter in book presented at the occasion of Peter van Koppen's valedictory lecture (March 17, 2022; postponed from 2020)

Bex, F. J., & Verheij, B. (2020). Stories about Evidence. Bakens in de Rechtspsychologie. Liber amicorum voor Peter van Koppen (Beacons in Legal Psychology. Liber amicorum for Peter van Koppen) (eds. Horselenberg, R., van Koppen, V., & de Keijser, J.), 309-327. Den Haag: Boom Criminologie. .

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