Alibi believability: Corroborator certainty, cooperativeness and relationship with the defendant

Alibi believability can be affected by characteristics of the alibi corroborator, including the relationship between the defendant and corroborator, which has been studied extensively by researchers. The corroborator's certainty that they were together at the time of the crime may also influence alibi believability, but only a few studies have examined this. Another factor that may affect believability is the corroborator's cooperativeness with the police, which is yet to be studied in the alibi context. Online U.S. participants recruited from CloudResearch (N = 280) acted as mock jurors and evaluated a mock arson case where the defendant used an alibi defence. The alibi corroborator's relationship to the defendant (brother/neighbour), the certainty that they were together at the time (65%/100%) and cooperativeness with police (cooperative/uncooperative) were manipulated between participants. The participants were evenly split when it came to verdict (p > .05) but were more likely to vote guilty when the corroborator was a brother rather than a neighbour (p < .01) and when the brother was uncooperative versus cooperative (p < .05). As expected, alibis were more believable when they were corroborated by a neighbour rather than a brother and when the corroborator was 100% certain that they were together versus 65% certain (ps < .01). Alibis were also more believable when the corroborator cooperated than when he was uncooperative (p < .01). Cooperative (vs. uncooperative) corroborators led to more positive defendant and corroborator views on all six character trait measures (ps < .01). Implications and future directions are discussed.