The ‘elasticity’ of criminal evidence: a moderator of investigator bias

This study examined investigators' perceptions of the reliability of incriminating and exonerating evidence of different types. Police trainees in the role of investigators read the background of a homicide case and then received a piece of evidence that either confirmed or disconfirmed their prior suspicion against the suspect. Despite identical objective characteristics of the evidence, participants rated the disconfirming (vs. confirming) evidence as less reliable and generated more arguments to question its reliability. This asymmetrical scepticism was stronger for participants judging witness evidence, compared to DNA and photo evidence, supporting the hypothesis that different types of evidence vary in ‘elasticity’—the extent to which subjective interpretations can be justified. Interestingly, the observed effects were not limited to the specific evidence in the case, but also affected the ratings of the type of evidence in general, suggesting that reliability criteria for witness information are highly malleable and sensitive to contextual influences. Copyright © 2008 John Wiley & Sons, Ltd.