Public domain film noir: Man Who Cheated Himself (1951)

IMDB

Wikipedia entry

Noir of the week entry

Full movie at youtube

Download or watch at archive.org

Director: Felix E. Feist
Writer: Seton I. Miller (story), Seton I. Miller and Philip MacDonald (screenplay)
Cinematographer: Russell Harlan

Plot:
A veteran homicide detective who has witnessed his socialite girlfriend kill her husband sees his inexperienced brother assigned to the case.

Trivia: Some put this film as 1950 instead of 1951.