The film's working titles were 29 Clues and The L.A. Investigator. Credits on the viewed print were missing; the above credits were taken from a cutting continuity deposited in copyright records. A written foreword on the viewed print states that this film was based on a case history taken from the detective files of the Los Angeles Police Department, with whose cooperation the film was made. HR further stated that the film, which had a "semi-documentary" style, was based on the murder of a highway patrolman by Erwin Walker, who had worked as a civilian for the Glendale Police Department. DV reports that Los Angeles police aided in research for the film, and that Sergeant Marty Wynn, credited on the screen as technical advisor, was a member of the force.
       A narrator introduces the audience to Los Angeles through a photographic montage in the film's opening, and uses the word “dragnet“ several times in the course of the film. Actor Jack Webb, who played a forensics expert in the film, developed a friendship with Los Angeles Police Detective Mary Wynn, who was the film's technical advisor. Winn, who was familiar with Webb because of his radio work, suggested that the actor start a new program using LAPD files and sticking close to real police procedures, much like the writers of He Walked by Night had done. Out of his experience on the film, Webb developed his own radio show, Dragnet, based on case files of the Los Angeles police, and became known for his characterization of Los Angeles police detective "Sgt. Joe Friday." Dragnet eventually became a popular NBC television series that ran intermittently from 3 Jan 1952 through Sep 1959 and was revived in a second series, which aired from Jan 1967 to 10 Sep 1970.
       As noted in modern sources, Anthony Mann, who directed Eagle-Lion's early 1948 semi-documentary release T-Men (see entry), completed the directing assignment on He Walked By Night for Alfred Werker. Several reviews lauded the film's final chase scene, shot in what NYT called "700 miles of hidden highways" that make up the giant underground tunnels of Los Angeles' storm drain system. He Walked by Night predated by more than a year The Third Man, a 1950 film (see entry) starring Orson Welles that also ended with a dramatic chase through the sewer system of a city (Vienna, Austria). The Los Angeles storm drains were used again in Them! (1954, see entry).
       Although the eponymous character, “Davis Morgan,“ is fatally shot at the end of He Walked by Night, his real-life inspiration, Erwin Walker, was captured by the LAPD. He spent time on death row, was institutionalized for many years in a state hospital, and finally won his freedom several years before his death in the 1980s.