Motivational sources of confirmation bias in criminal investigations: the need for cognitive closure

In two experiments, criminal investigators (N = 50) and undergraduate students (N = 68) read a set of facts from the preliminary investigation of a homicide case. Participants' initial hypothesis regarding the crime was manipulated by providing background information implying that the prime suspect had a jealousy motive or that there might be an alternative perpetrator. Students displayed a framing effect, such that guilt was ascribed to the prime suspect only when a potential motive was presented, whereas investigators did so regardless of hypothesis, thus being less sensitive to alternative interpretations. Investigators' need for cognitive closure (NFC) moderated the effect of the hypothesis on perceptions of the strength of the evidence against the prime suspect; high (v low) NFC investigators were less likely to acknowledge inconsistencies in the material when presented with a potential motive, but were more likely to do so when made aware of the possibility of an alternative perpetrator. Interpretations are somewhat clouded by the fact that dispositional NFC did not seem to affect in a consistent manner participants' motivation toward the experimental task.