Examining How Suspect Veracity and Culpability Effect Interviewer and Interviewee Behaviour in Homicide Interviews

Abstract

This thesis examines the effect of suspect veracity (whether a suspect provides a truthful or deceptive account) and culpability (whether the suspect was subsequently found guilty of the offence) on police interviewing practices in homicide cases. These variables are treated as analytically distinct, addressing a common limitation in existing research, which has often conflated deception with guilt. The study focuses on how suspect veracity and culpability affects interviewer conduct and suspect responses in real investigative contexts. Homicide interviews were analysed due to their evidential complexity, consequential and legal seriousness, and the demands they place on interviewers. In contrast to research based on experimental or simulated data, this thesis draws on field data to provide insight into police interviewing as it is practised. The research is based on 60 audio-recorded homicide suspect interviews, totalling 113 hours of material. Four empirical studies systematically examined the effect of veracity and culpability using content analysis and structured coding frameworks. The first two studies investigated question and statement types, and suspect responses. The third and fourth examined the type and timing of evidence disclosure and the corresponding suspect behaviour. A fifth study, using questionnaire data from police officers, explored professional perceptions of the interview practices observed in the field data. Data were analysed using both quantitative and qualitative methods, including descriptive and inferential statistics and thematic analysis. Findings indicate that veracity and culpability affected interviewer behaviour across all stages of the interview. Suspects who deceptively denied their culpability were more frequently challenged, through both questioning and increased evidence disclosure. In contrast, truthful suspects who admitted culpability were met with clarification-based questions, reflecting a more collaborative, narrative-focused approach. Furthermore, suspects who truthfully denied culpability may present interpretive challenges, as their honesty could be less apparent perhaps due to limited knowledge, cautious responses, and misplaced confidence in being believed. While recommended practices were generally followed, the limited use of open questions and variability in evidence disclosure suggest areas for further development. The thesis contributes to the field by providing empirically grounded insights into how suspect veracity and culpability affect interviewer and suspect decision-making in serious crime contexts.