The Phantom of 42nd Street (1945)

An actor is killed during the performance of a play and critic Tony Woolrich (Dave O'Brien) undertakes to solve the crime. Claudia Moore (Kay Aldridge, in her last movie role), the girl he loves, is suspected, but when two more deaths occur, she is also threatened by the Phantom Killer. During a production of "Julius Caesar" the killer makes a final attempt.