He Walked by Night is a 1948 black-and-white police procedural film noir, directed by Alfred L. Werker and Anthony Mann. The film, shot in semidocumentary tone, was loosely based on newspaper accounts of the real-life actions of Erwin "Machine-Gun" Walker, a former Glendale California police department employee and World War II veteran who unleashed a crime spree of burglaries, robberies, and shootouts in the Los Angeles area during 1945 and 1946.
During production, one of the actors, Jack Webb, struck up a friendship with the police technical advisor, Detective Sergeant Marty Wynn, and was inspired by a conversation with Wynn to create the radio and later television program Dragnet.
He Walked by Night was released by Eagle-Lion Films and is notable for the camera work by renowned noir cinematographer John Alton. Today the film is in public domain.