I Cover the Underworld (1955)

John O'Hara, a divinity priest student endeavors to help the police, rolling up a gang of criminals. John poses as his twin brother Gunner O'Hara a gangster, who is in prison. John is finally accepted by the gang and he succeeds improving the efficiency of this gang by cooperating closely with other criminal gangs. John coerces them these gangs, keeping careful records of their various criminal activities. Problems for John and the police arise when Gunner O'Hara escapes from prison.