He Walked by Night (1948)

Whit Bissell, Ann Doran, Kenneth Tobey, John Dehner

In post WW II, Los Angeles, a cop's killed in the middle of the night. With no leads, the chief of police assigns Sgts. Jones and Brennan to investigate and apprehend the killer. They target low-level criminals, such as Paul Reeves, hoping he'll lead them to bigger fish, specially, the one who shot