The Man who cheated himself (1950) Lee J. Cobb, Jane Wyatt and John Dall

Wealthy socialite Lois Frazer, divorcing her fortune-hunter husband, Howard, finds a gun he had 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. Cullen takes control, discarding the weapon and moving the body. Cullen ends up assigned to investigate 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.