How very sad and how very horrible are some posts. I was brought up by loving, kind, responsible, respectful parents, who taught manners, respect, love & kindness. My younger brother has had the EXACT same upbringing as myself.
He has stolen from all of us as a teenager, he has robbed, been in prison and is a functioning drug addict. This is not my parent's doing, this is the peers he hung around with, he doesn't care about anyone, hasn't done for years.
OP's problem is extremely serious and unacceptable. Have you made clear in BLACK AND WHITE ( and i'm sure you have) that he can no longer live with you/family if his behaviour continues. If you have AND it continues, you have done as much as you possibly can. He MUST know that his actions have consequences and that means he no longer stays at home. You have tried with the police, CAMH's School.
The Local Authority have an obligation to ensure you and your youngest are safe.
I am sure initially he will be even more furious, even more violent, try to gain entry etc. At 12 and in the eyes of the law, he IS responsible for his actions.
Let him know, he most certainly can come home and you love him when it stops. At the moment, you will no longer tolerate his abuse, being his mother does not mean you have to put up with it.
A shock to his system and to know you will absolutely follow through, may make him realise what he is about to lose.
Good Luck OP, please do update us 