The Stranger Wore a Gun (1953)

Having been a spy for Quantrill's raiders during the Civil War, Jeff Travis thinks he's a wanted man and flees to Prescott, Arizona where he runs into Jules Mourret, who knows of his past. He takes a job on the stage line from which Mourret is trying to steal gold. When Mourret's men kill a friend of his, he sets out to get Mourret and his men. When his plan to have another gang get Mourret fails, he goes after them himself.