Police and Prosecutors’ Perceptions of Adult Sexual Assault Evidence Associated with Case Authorisation and Conviction

This study examined the association between the quality of verbal evidence in cases of sexual assault reported by adults and professionals’ (police and prosecutor) ratings of the likelihood that the cases will result in a conviction at trial. Sixteen police detectives and 19 prosecutors (all specialists in sexual assault) each read two mock sexual offence briefs of evidence, one of a case involving rape of an adult and the other involving an adult reporting historical child sexual abuse. For each case type, two versions of the briefs were developed with regard to evidence quality, which varied according to the degree of elaboration in the responses by the witnesses and suspect, and contextual evidence. Participants rated the likelihood of proceeding with a case and conviction (on 10-point likert scales) and provided a rationale for their decisions. Almost all of the participants agreed that the cases would proceed to court. However, the likelihood of conviction was not associated with the likelihood of proceeding to court, or the evidence quality of the briefs. Differences were found in both the ratings of proceeding to court and conviction, and the factors underpinning the ratings across the two professional groups. The implications of the findings for police organisations are discussed.