Choice and Background Knowledge: How do Individuals Evaluate Accumulating Evidence in A Murder Scenario?

Abstract

Can the simple act of selecting a possible suspect of a crime bias the evaluation of the evidence? Does the typicality of the crime impact the assessment of guilt of a suspect? In two experiments, we examine these two questions and find some remarkable results with implications for law enforcement and jury deliberation. Experiment 1 data show that by allowing participants to choose a most-likely-perpetrator, guilt ratings were substantially higher compared to participants who were not allowed to make a choice. This difference persisted after reading a further body of incriminating evidence. In experiment 2 participants were provided with general and specific background information relevant to a suspect, in other words how common was the crime-suspect scenario. When provided with high plausibility compared to low plausibility information, participants gave higher guilt ratings that persisted after further evidence. The results are interpreted in terms of argument theory which provides a parsimonious explanation of the data. These results have implications for the conduct of investigations, for example: putting in place procedures that minimize the effects of suspect prioritization and background information.

A taxometric approach to base-rate estimation and idiographic classification in psycholegal research.

“…The wealth of research on the underlying causes of wrongful conviction shows that evidence is fallible and cannot be trusted to distinguish guilt from innocence with perfect accuracy (The Innocence Project, 2022; The National Registry of Exonerations, 2022). Relatedly, literature on investigative decision-making reveals that obtaining one piece of evidence can affect the likelihood that investigators will seek out and obtain additional pieces of corroborating evidence, producing dependencies in the evidential record (Kassin et al, 2013; Mackenzie et al, 2018; O’Brien, 2009; Rassin et al, 2010). Indeed, such relationships—investigative decisions informed by existing evidence—are frequently considered the hallmarks of investigations conducted correctly.…”

“…TAXOMETRICS IN CRIMINAL JUSTICE AND LEGAL SYSTEMS Mackenzie et al, 2018;O'Brien, 2009;Rassin et 2010). Indeed, such relationships-investigative decisions informed by existing evidence-are frequently considered the hallmarks of investigations conducted correctly.…”