Behind Locked Doors (1948)

A well-known judge has become a fugitive from the police, with a large reward on his head. A reporter believes that the judge is hiding in a private sanitarium, so she seeks out a private investigator and asks him to pretend to be insane, so that he can get inside the sanitarium and look for the judge. The investigator is admitted to the asylum, and encounters many dangers while trying to prove that the judge is there.