Devil's Cargo (1948)

Conroy, a playboy, is found shot to death in his penthouse. A ne'er-do-well named Ramon Delgado (Paul Marion) tells the Falcon, Michael Watling (John Calvert), that he committed the murder and asks the Falcon to keep a key for him until after he has been acquitted. He says he feels certain of an acquittal when the police learn that the motive for the killing was Conroy's attention to Delgado's wife, Margot (Rochelle Hudson). Tom Mallon (Theodore von Eltz) enters the case as Delgado's attorney, but after Delgado is found poisoned in his jail cell, the Falcon suspects Mallon of killing his own client.