Assessing the Reliability of Multiple-Showup Procedures With a Single Eyewitness
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In this program of research I examined the influence of multiple-showup procedures on the reliability of eyewitness identification. If an eyewitness rejects a suspect from a showup, law enforcement personnel may search for new suspects, and if a new suspect is found, they may run another showup with the same eyewitness. Law enforcement personnel may go through several iterations of finding suspects and running showups with the same eyewitness for single-perpetrator crimes (Chapter 3, Study 1). The use of multiple-showup procedures with the same eyewitness increased innocence risk (Clark & Godfrey, 2009), the probability that a suspect was innocent given identification (Chapter 3, Studies 2 and 3). The increase in innocence risk was primarily attributable to the fact that innocent suspect identifications cumulate when law enforcement personnel use multiple showups in single-perpetrator crimes. Although pre-showup instructions decreased innocent suspect identifications, innocence risk remained unacceptably high (Chapter 3, Study 4; Chapter 4). On a more positive note, pre-showup instructions intended to reduce eyewitness’ perceptions of scarcity (belief that they may not have another opportunity to identify the perpetrator) decreased innocent suspect identifications over and above a may-or-may-not be present admonition (Chapter 4). Scarcity instructions may prove useful in identification procedures, more broadly. I argue that an identification from a multiple-showup procedure is not reasonable evidence of guilt; however, practical constraints may require that law enforcement personnel sometimes show eyewitnesses more than a single showup. A stronger partition between investigative and evidentiary procedures is recommended (Chapter 5).