He Walked by Night (1948)

Plot summary written in 1988, now saved for posterity.

A policeman on night patrol is brutally murdered while on duty one night, and his colleagues try to find the criminal. The first big clue comes when the criminal sells stolen electronic equipment. When he shows up to collect the money, the police tries to capture him, but fails. Several persons who had been robbed by the bandit help to make a composite sketch of his face. On account of the technique and the knowledge of police procedure displayed by the bandit, one policeman believes that he belongs or belonged to the police force. It is discovered that he belonged to the department of radio technicians of the police. It is discovered that he probably lives in Hollywood (here I am not completely sure). One of the policemen disguises as a milkman and begins an investigation in Hollywood. He obtains from one of the local dwellers the information of the house where the criminal supposedly lives. When he delivers milk at that house, the policeman breaks the milk bottle on purpose. The criminal goes outside to see who is there, and is recognized by the policeman, because of the similarity to the sketch. The policeman doesn't do anything immediately; he sends for the help of his colleagues in order to make the arrest. Even with his house surrounded, the criminal enters a sewer hole. Then a chase begins inside the sewer system, at the end of which the chased man is killed.