I agree with Anya completely. I had a friend who met one of these types on an internet dating website. I was aghast when after only seeing him for four months they ended up living together (she moved him in). They then got engaged, I and other friends tried to tell her to be wary, to no avail.
It was only after he moved in that the trouble started. My friend was a vivacious, funny and fun-loving lady. He completely killed her confidence, personality and her ability to judge situations for herself.
My friend had run businesses and had a damn good brain, she became a shadow of her former self.
He was a superb actor, my friend's family all thought he was wonderful. I tried to broach things with the family about my concerns, but was told where to go.
In the end he destroyed my friendship with her and others. One of her other friends went to visit her one time (in their new house, that he persuaded her to move to) and was shocked at how downhill she had gone. I will never forget my friend, it has left me very wary of internet dating sites to this day. My friend passed away a long time ago, we only kept in touch by Christmas Card and phone latterly, but I believe I was lucky to have that much contact. At her funeral he cried all his 'crocodile tears'. I left early with another friend as we were both so sickened by the whole thing.
The only thing I will say is this - my friend's family who were close to her did not see this man for what he was. He hid it extremely well, along with my friend. How on earth they will ever prove these cases in a court of law I do not know. I tried to help my friend and was practically called a liar. The other thing you have to remember is , the partner suffering the abuse will support/ cover up things at all costs. The other factor in my friend's case was, she was older and told me she did not want to be alone. So very sad. I feel he destroyed her.