Alcatraz Island (film)

Rackateer Gat Brady is on trial for cheating the government. He makes a deal with the prosecutor who will recommend a six-month sentence in jail in exchange for a guilty plea. The judge tosses out the plea agreement and gives Gat five years in prison. His girlfriend Flo Allen promises to wait for him and to look after Gat's daughter. Gangster Red Carroll snatches the girl for ransom. He's caught and sentenced to the same prison as Gat Brady. They quickly fight and Brady is blamed. Later on they are both transferred to another prison where Red is stabbed and killed with a work knife. Brady is put on trial for the murder. Defending him is the man in love with his daughter, the guy from the New York DA's office. A friend of Gat's from prison talks another con into taking credit for the crime and Gat is acquitted. Just as the guilty verdict is about to be read we discover that Gat's convict friend is actually a FBI agent who has a recoding of the killer's confession made just before he hanged himself.