"Alfred Hitchcock Presents" The Big Switch (1956)

Chicago, 1920: Gangster Sam Dunleavy has just returned to town, and is visited by Al, a former childhood friend who is now a police officer. Al knows that Sam's girlfriend has just dropped him, and he warns Sam not to try anything violent. But Sam does plan to kill his ex-girlfriend, and he knows he needs an alibi. He sees his friend Barney, who promises to give him a perfect alibi for $2500. They work out the details, and Sam returns to Barney's place later to put the plan into action. But Al also shows up, so Sam knows that the plan must work perfectly.