Jimmy is the serial killer. After the chase at the beginning of the movie, where Tom's (Bruce Willis) father dies, Tom's uncle (Jimmy's father) discovers that Jimmy is the killer and lets him go. Jimmy's father accidentally killed Tom's father when Tom's father was going to kill Jimmy. The family members meet at a cabin and Jimmy's father shoots Jimmy but he's wearing a vest. Jimmy kills his father and runs away. Tom catches up, they fight, Tom gains the upper hand and kills Jimmy with a taser.