Date of Award

5-2026

Degree Type

Thesis

Degree Name

Honors Thesis

Department

Psychology

First Advisor

Stacy Wetmore

Second Advisor

Mark Suchyta

Abstract

The present study is only the second investigation to examine the effects of accomplice witness testimony on jury decision making. For this study, participants read a trial transcript of an assault case in which the defendant was accused of starting a physical altercation. Participants were randomly assigned to one of three conditions where we varied the level of involvement of the accomplice. The three conditions included Accomplice-Altercation where the accomplice was directly involved in the altercation and threw a few punches, Accomplice-Lookout where the accomplice served as a lookout for police arrival, and a No Accomplice condition. The results of the study revealed that participants were more likely to vote guilty when an accomplice was present compared to the no accomplice condition. Participants were also more likely to vote guilty in the altercation condition compared to the lookout condition and no accomplice condition. Furthermore, participants were more likely to charge the accomplice in the altercation condition compared to the lookout condition. Surprisingly, we found no significant difference in terms of credibility rating in the altercation and lookout condition. Participants appeared to be succumbing to the fundamental attribution error (the tendency to overemphasize internal motivations over external motivations), as seemed to focus on the disposition of the accomplices (e.g., they are trying to tell the truth now) rather than the situational factors (e.g., plea deal) regarding their criminal involvement. This study raises important policy concerns and signals a need for courts to reassess protections surrounding the use of different informants as well as a call for future research specifically focused on accomplices.

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