The Man Who Cheated Himself (1950)

Wealthy socialite Lois Frazer, divorcing her husband, Howard, finds a gun he's bought. She kills him with it in front of the new man in her life, Lt. Ed Cullen, a homicide detective with the San Francisco police.

The twice-married Lois manages to manipulate Cullen into disposing of the murder weapon and moving the body. Cullen ends up investigating the case, assisted by kid brother Andy, who is new to the homicide division and delays his honeymoon to keep working on his first big case.

The gun is found and used in another killing by a young punk, Nito Capa, so all Cullen can think to do is try to pin both crimes on him. Andy Cullen keeps connecting Ed to the first murder, however, catching him in a number of lies.

Ed ties and gags Andy and tells Lois they need to flee. Roadblocks seal off the city, but Andy has a hunch where Ed took the woman to hide, near the Golden Gate Bridge, and soon they are under arrest. Outside the courtroom, Ed overhears Lois offering to do anything for her lawyer if he can keep her from being convicted.