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Memory-Based Approaches to the Examination of Alibis Provided by Innocent Suspects

Doctoral thesis
Authors Shiri Portnoy
Date of public defense 2019-03-01
Opponent at public defense Professor Robert A Nash
ISBN 978-91-7833-327-1 (PDF); 978-91-7833-326-4 (Print)
Publisher BrandFactory
Place of publication Göteborg
Publication year 2019
Published at Department of Psychology
Language en
Keywords Alibis, Innocent suspects, Investigative Interviewing, Memory
Subject categories Psychology


The aim of the current thesis was to extend research on suspect alibis by exploring how the process of providing alibis may be improved for innocent suspects, for 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 enhance innocent mock suspects’ memory output when reporting past actions (Study I) and evidence that may corroborate their alibi (Study II); (ii) whether a presumption of guilt, communicated to innocent mock suspects by an interviewer prior to providing their alibi, affects their memory output (Study III); and (iii) the beliefs and knowledge of lay people about factors concerning the processes of alibi generation and provision (Study IV). In Study I (N = 192), innocent and guilty mock suspects provided an alibi, reporting about recently completed tasks. Prior to alibi provision, participants were asked to maximize their alibi accuracy, informativeness, or both; control participants were given no accuracy or informativeness instructions. Innocent mock suspects who were instructed to provide an accurate and in-formative alibi provided the largest number of correct details compared with control participants. In contrast, for guilty mock suspects, neither the number of correct details nor the accuracy of the alibis differed as a result of pre-alibi instructions. In Study II (N = 78), 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 asked only 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 control participants. However, instructions focused on accurate and informative reporting about past actions and corroborating evidence did not result in a larger number of correct details compared with instructions to re-port accurately and informatively about past actions only. In Study III (N = 90), innocent mock suspects provided an alibi to an interviewer who communicated to them that she believed in their guilt or innocence, or had no belief about their involvement in a crime. Participants detected the innocent/guilty presumption of the interviewer, but the number of correct details provided in their alibis did not differ across interviewer-belief conditions. Finally, in Study IV (N = 343), lay people from the United Kingdom, Israel, and Sweden responded to a series of questions regarding their beliefs about the generation and provision of alibis. Participants tended to believe that innocent suspects do not provide inaccurate alibis, but that should this happen, memory errors may be the primary reason. Participants also tended to believe that interviewers begin to form their opinion of the guilt or innocence of suspects prior to or while hearing the suspects’ alibi for the first time, and that a presumption of guilt 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 suspects to provide more correct information may result in innocent suspects providing more forensically valuable information which may in turn promote their exoneration. The finding that participants detected the innocent/guilty presumption of the interviewer suggests that the effect of a presumption of guilt on innocent suspects’ alibis should be examined in longer interviewer-interviewee interactions. Lastly, the findings of the survey demonstrate that lay people hold some mistaken beliefs about the ability of innocent suspects to provide accurate alibis. The current thesis demonstrates the merits of examining innocent suspects as a unique group of rememberers and basing such examination on memory theory.

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