I Take This Oath (1940)

Steve Hannigan, joins the police force as a rookie after his father, a veteran policeman, has been murdered by a bomb placed by racketeers. Steve intends to find the gang-leader responsible for his father's death. He frequents gangster hangouts, searching for a clue, and starts to neglect his Police-school classes, where he is training under the supervision of his sweetheart's father, Captain Casey. He temporarily loses his police badge, but continues his quest.