Psychopath?

Yeah, that's definitely not normal. I'd bring this up with your parents if you haven't already. If he starts doing this to other animals, you should really start to worry. If your parents don't care about his behavior, you should bring this up with another family member or a friend. Live with one of them if your parents still don't do anything. You don't need permission. It's better than potentially getting killed. Maybe let one of your family members or friend's parents help take care of the situation.

If none of that is an option, keep something in your room for self-defense and move out ASAP. Don't die pls.