When the police do a test drive to see if Chick had enough time to commit the crime of which he is accused, they drive from the starting point to the crime scene, then turn around and drive back. They have not allowed any time for him to have committed the crime.
When Eleanor Griffith finds out that Regis Toomey is a police informer, she tells him that she won't give him away as long as he does nothing to harm her boyfriend. This makes no sense, as his reason for remaining friendly with the gang is to collect evidence against him--as, indeed, he does.
Tommy tells Joan that he has loved her ever since they were kids together, but he looks much older than she, and in fact the actor who plays him is twelve years older.