Hm..this is tough. You could report him to the police, although this could make her angry against you, or she might not be angry, she might be relieved. She might not have told the police because he could abuse her more for telling on him. It must hurt seeing a good friend who you consider as being part of your family in this situation. You could try The Jeremy Kyle Show, I'm serious, this could get resolved, Jeremy Kyle is great at what he does and could give her boyfriend help to calm him down, or speak to your friend and tell her that he's not worth it.
I really hope everything works out ok, and hope your friend recovers quick.