Autistic/Downs Adult Brother Increased Agression

My adult brother who is 32 lives with my father. My father is a diagnosed narcissist, and my whole family has basically had to cut ties with him. I'm the only one who really has any kind of communication with him.

Within the past few years, my brother has been developing aggressive behavior, hitting people at home and in public. My mother and I think that it's because my father is being negligent in his care for him, but there's no real way to confirm this. APS in the town where he lives is criminally incompetent (their director doesn't even have a high school diploma) and the police haven't been much help either.

My question is, why is my brother suddenly developing these behaviors? Does anyone else have experience with this?