The movie took loose inspiration from the Ed Gein case. Ed Gein was the model for Norman Bates in "Psycho" and the Buffalo Bill character in "Silence of the Lambs."
It's presented as a true story, but it's actually fiction. That said, the story is based on that of notorious serial killer and grave robber Ed Gein, who was also a source of inspiration for Hitchcock's Psycho.
