Supernatural - Born Under A Bad Sign Season 2 Episode 14

Sam, who had been missing for over a week, frantically contacts Dean and Dean hurries to be with his brother. There he finds Sam covered in blood, but he can't remember what happened that caused the blood to be spatted on him. As the brothers search for the truth, they're shocked to find a tape that shows Sam killing a fellow hunter, making Sam think that his evil side is taking over his body.