For Them That Trespass (1949)

Christy Drew, an aspiring young writer trying to broaden his experience, gets involved with Frankie Ketchen and her two suitors, Herb Logan and Jim Heal. One night, Jim finds Frankie has been with Christy and kills her. Herb is accused of the murder and sentenced to prison. After he gets out, he blames Christy but finally proves Jim to be the real killer, based on a clue provided to him by Christy, now a famous writer.