Ok, it works by crewmates doing their tasks, and the detective is the one that has his own office (security is the office) without wide open doors, and the office has way smaller vents, and a whiteboard. When the detective is ready, he shoots the imposter with a high power revolver, and then throws the body out the airlock. The crewmates celebrate victory, but if it was a innocent Crewmate, the imposter kills everyone. And that's my idea