Imagining counterfactual versions of past events can distort memory. In 3 experiments, we examined whether imagining a false alibi for a mock crime would make suspects appear less guilty in a concealed memory detection test, the autobiographical Implicit Association Test (aIAT), which aims to determine which of 2 autobiographical events are true. First, "guilty" participants completed a mock crime, whereas "innocent" participants completed an innocent act. Next, some of the guilty participants were asked to imagine a false alibi that corresponded to the innocent act. Finally, all groups completed the aIAT. Across experiments, we varied the type of aIAT used and also compared the effectiveness of the false alibi countermeasure when only imagined once, versus when it was repeatedly imagined over a week-long period. The aIAT accurately detected the mock crime as true for guilty participants without a false alibi, but was consistently less able to detect the mock crime as true for guilty participants who had imagined a false alibi. The findings suggest that if guilty suspects fabricate an alibi, this may create a memory for the alibi that appears to be true based on the aIAT, which is problematic for its real-life applications in concealed memory detection. (PsycInfo Database Record (c) 2020 APA, all rights reserved).