First of all, good on you for being a good person and a good friend, AJ.
Secondly, as you probably know, I am a child and adolescent of abuse and I cannot take it when I see abuse up close: my normal reaction is to walk up to the person dishing it out and say "Do you want to have a go at me? Take your best shot, but if you touch me, be aware that you better put me down good because if I get up, I will kill you."
Thirdly, I would suggest that you confront this bastard and give him a piece of his own medicine - bullies like this and people like my birth parents are usually cowards and have no fight in them.
Get your friend to have this person arrested: I sincerely hope the cops tazer him in the nuts for all the abuse he has heaped on your friend.
Dammit, I HATE abusers!!