Fingerman (1955)

Treasury agents, desperate to get evidence on syndicate kingpin Dutch Becker, give ex-con hood Casey Martin a choice: life in prison or courting sudden death as a government "finger man." When he discovers that his sister is now a drug addict because of Becker, Martin agrees to go undercover. Becker's chief aide is sadistic Lou Terpe, Martin's former cellmate, whom he detests the sight of, and the danger hanging over Martin expands to threaten those around him