1x20 Dead Man's Blood

When an old vampire hunter is targeted by a group of vampires, he tries to attack them with an old Colt pistol, but is killed before he can fire a shot. Returning to the nest, the vampire Kate (Anne Openshaw) gives the Colt to her mate, the leader Luther (Warren Christie). When Dean recognizes the murdered hunter's name in the newspaper, he and Sam head to Boulder, Colorado, and discover a letter addressed to their father, who suddenly returns. The letter reveals to him that the gun is mystical and capable of killing anything. Realizing that they can use it to finally kill Azazel, the demon responsible for their mother's death, the Winchesters capture Kate and attempt to trade her to Luther in exchange for the gun. During the negotiation, Luther attacks John, and the brothers intervene. John retrieves the gun, and the legend of the Colt is proven to be true as he shoots Luther dead.