Memory-based approaches to the examination of alibis provided by innocent suspects

  • Shiri Portnoy

Student thesis: Doctoral Thesis


The aim of the current thesis was to extend research on alibi provision by exploring how this process may be improved for innocent suspects, to whom the provision of inaccurate and incomplete alibis may be detrimental. Across three experimental studies and one exploratory survey, I examined (i) whether memory-based reporting instructions enhanced innocent mock suspects’ memory output when reporting about past actions (Experiment 1) and evidence that may corroborate their alibi (Experiment 2); (ii) whether a presumption of guilt communicated to innocent mock suspects by an interviewer prior to providing their alibi affected their memory output (Experiment 3), and, (iii) the beliefs and knowledge of lay people about factors concerning the processes of alibi generation and provision (Survey). In Experiment 1, innocent and guilty mock suspects provided an alibi, reporting about recently-completed tasks. Prior to alibi provision, participants were asked to ensure that their alibi was either accurate or informative, or both; control participants received no accuracy or informativeness instructions. Innocent mock suspects who were instructed to provide an accurate and informative alibi provided the largest number of correct details compared with control participants. In contrast, for guilty mock suspects, neither the number of correct details provided nor the accuracy of alibis differed as a result of the pre-alibi instructions. In Experiment 2, prior to providing an alibi, innocent mock suspects were asked to report accurately and informatively about past actions during task completion or about past actions and corroborating evidence. Control participants were only asked to report about their time while away from the lab. Results indicated that participants who were asked to report accurately and informatively about past actions or about past actions and corroborating evidence provided a larger number of correct details than did control participants. However, the instructions focused on accurate and informative reporting about past actions and corroborating evidence did not result in the largest number of correct details. In Experiment 3, innocent mock suspects provided an alibi to an interviewer who communicated to them that she believed that they were guilty or innocent, or had no belief about their involvement in a crime. Participants perceived the innocent and guilt presumptive approach of the interviewer, but the number of correct details provided in alibis did not differ across interviewer-belief conditions. Finally, in the survey, lay people from the United Kingdom, Israel, and Sweden responded to questions concerning the generation and provision of alibis, indicating their beliefs regarding impaired memory processes as possibly underpinning inaccurate alibis by innocent suspects and the issue of interviewers’ presumption of guilt. Participants tended to believe that innocent suspects may not provide inaccurate alibis, but that should this happen, memory processes may be the primary reason. Participants also tended to believe that interviewers usually begin to form an opinion regarding the guilt/innocence of suspects prior to or while hearing the suspects’ alibi for the first time, and that guilt presumption can affect how interviewers conduct interviews. The findings reported in the present thesis suggest that innocent suspects’ memory output may be increased using specific memory-based pre-alibi instructions. Guiding suspect to provide more correct information may result with innocent suspects providing more forensically valuable information that may promote their exoneration. The finding that participants perceived the innocent and guilt presumptive approach of the interviewer suggests that the effect of guilt presumption on innocent suspects’ alibis should be examined during longer interviewer-interviewee interactions. Lastly, the findings of the survey demonstrate that lay people hold some mistaken beliefs regarding innocent suspects’ ability to provide accurate alibis. Throughout this thesis, I discuss the importance of examining innocent suspects’ memory output as a unique group of rememberers and emphasise that such examination should be based on memory theory.
Date of AwardSept 2018
Original languageEnglish
SupervisorLorraine Hope (Supervisor)

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