Castle (2009): Season 6, Episode 16

6 - 16: Room 147

When a guilt-ridden young woman confesses to the murder of a struggling actor -- knowing details only the killer could know -- Beckett and Castle seem to have an open-and-shut case, until they uncover proof that their suspect couldn't possibly be the killer. When a second person confesses, equally convinced they committed the murder, the team realizes the case is far more mysterious than they thought.