Truth-tellers stand the test of time and contradict evidence less than liars, even months after a crime

When deceptive suspects are unaware of the evidence the police hold against them, they contradict that evidence more than truthful suspects do – a useful cue to deception. But given that, over time, truthful suspects might forget the past and also contradict the evidence, how effective are lie detection techniques that rely on such inconsistencies when suspects are questioned months after a crime? In Experiment 1, people committed a theft (liars) or a benign activity (truth-tellers) in a university bookshop. Shortly after or two months later, we questioned them about their bookshop visit without informing them of the evidence implicating them in the theft. Though truth-tellers contradicted some evidence after both time delays, liars always contradicted the evidence more than did truth-tellers. In Experiment 2, we presented the mock suspects’ responses to an independent group of laypeople and asked them to rate how deceptive the suspects were. Laypeople rated liars as more deceptive than truth-tellers after both time delays, but also rated truth-tellers questioned two months after the crime as more deceptive than truth-tellers questioned shortly after the crime. These findings suggest that liars’ tendency to distance themselves from a crime might outweigh any memory decay that truth-tellers experience in the two months following a crime. As a result, the extent of a suspect’s contradictions with the evidence could still be diagnostic of deception even after an extended time delay.