Sleepwalker - S2.E15

Gruesome, unmotivated killings soon begin to take place in a small town after a man finds the Dead Man's Gun, and soon he become convinced that he is performing the deeds himself while sleepwalking. His wife stays awake to watch him, but falls asleep early and another murder takes place. The man is incredibly guilty for what he's done, turns himself in, and is sentenced to die ... but is he the real culprit? No, he's not. His wife is!