This is one of my favorite western series, but "The Brothers" episode seems like sort of a ripoff of an Alfred Hitchcock Presents episode from six years earlier titled "Revenge".

WARNING: SPOILER ALERT

In "Revenge" Vera Miles plays a woman who was assaulted. She has her husband drive around with her looking for the perpetrator. Eventually she says, "That's him!" Her husband kills the man. Later, while they are driving around again, she once again says, "That's him!". That's when her husband realizes she's lost it and is just pointing out random men. Thus he's murdered an innocent man.

In "The Brothers" episode, the old prospector kills Buddy Ebsen's character (whom Paladin was trying to bring back for a murder trial), insisting he's his brother, who also stole the prospector's ore, kidnapped his mining partner and then left his mining partner to die in the desert. Later, as Paladin and the prospector are riding in the latter's wagon back to civilization, they come across a stranger and chat for a moment. As the stranger is leaving, the old prospector says, "That's him!". He thinks he's his brother again. It turns out that the stranger and Buddy Ebsen's character are both left handed, and that's the main reason he picks them out as the killer each time. Paladin finally realizes the old man has lost it.