An alibi is a statement that places a defendant elsewhere at the time of a crime (Nolan & Nolan-Haley, 1990). Alibis are studied empirically due to the number of innocent people who had alibis but were wrongfully convicted (Heath et al., 2021). Person alibi evidence is evidence involving a corroborator, and it is frequently used in actual cases (Dysart & Strange, 2012). This study investigated two alibi corroborator characteristics: certainty and cooperativeness. Only one study has empirically studied alibi corroborator cooperativeness, and the authors found that when a corroborator was cooperative with police (versus uncooperative) the alibi was more believable (Allison & Kollar, 2023).

320 participants recruited from CloudResearch read a description of a theft, police investigation, and trial. They were randomly assigned to one of eight conditions in a 2 x 4 between-subject design. Half of the participants read a police investigation in which the alibi corroborator was cooperative with police by returning their calls and half read one in which the corroborator was uncooperative with police. Participants then read that the corroborator was questioned twice about how certain he was about being with the defendant. The corroborator’s certainty was maintained either high (100%-100%) or low (75%-75%), strengthened (75%-100%), or weakened (100%-75%). Next, participants completed a questionnaire where they rated the alibi’s believability, the defendant’s character, and the likelihood of guilt.

Alibis were more believable when the corroborator cooperated with police than when he did not. Alibis also were more believable when the corroborator’s certainty was maintained and high than when it was maintained and low. The defendant was seen as more likely to be guilty when the corroborator did not cooperate with police than when he did cooperate. Lastly, the defendant was viewed more positively when the corroborator cooperated versus when he did not.