The Virginian Season 9 Episode 6 Gun Quest

The Virginian is taken by a posse, brought into a saloon in a small town, tried before an incompetent drunken judge, convicted of murder, and taken out to be hanged, all in a span of a couple hours. The only evidence allowed is the accusation of the dead man's son, who claims The Virginian is a notorious hired killer known as Boss Cooper, and that he saw him kill his father. The Virginian escapes from the lynch mob and determines to clear his name by finding the real Boss Cooper, though the dead man's sons are trailing him.