The story is some chick and her husband move back to her old hometown;
The chicks old high school boyfriend ends up raping her with his pals .
The local town retard kills the mayors daughter or some and hides out in the couples home, then the rapist/old boyfriend and his pals go on an attack of the house, ending up with all of their murder .

Your looking for Straw Dogs

http://en.wikipedia.org/wiki/Straw_Dogs_(1971_film)

http://en.wikipedia.org/wiki/Straw_Dogs_(2011_film)