Sling Blade(1996)

The tale of Karl Childers, a mildly retarded man faced with a complex moral dilemma. As a child, Karl was severely abused by his fanatically religious parents, who considered him a punishment from God. When he found his mother sexually entangled with the town bully, Karl believed their actions were wrong--and killed them, swiftly and brutally, with a sling blade. Now, against his will, Karl has been released from an asylum to return to society after twenty-five years. A gifted mechanic, Karl finds work in his small Southern hometown, where he meets young Frank Wheatley. Frank is the first person ever to accept him without fear or judgment; the two become instant friends, and Frank convinces his mother Linda to let Karl live with them. But there's trouble in the Wheatley home: Linda's abusive, narrow-minded boyfriend. Groping to reconcile his own simple moral code with everything he has been taught about right and wrong, Karl must decide whether to stand by and watch, or step in to protect Frank.