What movie is about a mentally slow man who kills his family as they have treated him like an animal trough years and when released he becomes friends with boy mother in small village?

You're likely thinking of the 1994 film "The Simpleton" (also known as "The Simple Man").

Here's a summary:

* Plot: The film tells the story of a mentally challenged man named Dimitri who is abused by his family. He eventually snaps and murders them, but is eventually released due to his diminished capacity. He then ends up in a small village where he befriends a young boy and forms a bond with the boy's mother. However, his past trauma and the way he is perceived by others continue to haunt him.

This film explores themes of innocence, violence, and the complexities of human connection. It's a powerful and disturbing film, though it's not widely known.