I Was a Shoplifter (1950)

Police detective Sergeant Jeff Andrews is working on a case involving a gang of shoplifters, and he allows himself to be falsely arrested as a petty thief in order to make contact with the gang. Meanwhile, Faye Burton, a petty shoplifter and the daughter of a prominent judge, is blackmailed by the gang into joining them on the promise that they will retrieve a confession signed when she was caught by a department-store detective who had her sign the document rather than calling the police. Jeff and Faye take a lot longer to figure out who is the "brains" behind the shoplifting gang than the audience does--and the audience has less information than they do.