This, unfortunately, was his last, and most dramatic, controlling act. The only other way he could have been in even MORE control would have been to kill your daughter, also. I know you realize how fortunate you are that he did not exercise ultimate control in this situation. And, his mother is so wrapped up in her grief that she cannot see this. If not now, it would have happened later. If not in reaction to your daughter, to someone else's daughter. And IF (this is a big if) your DD had NOT broken up with him, and had gone on to marry(or not) and have children with him, his anger might be directed out at his children, also. Or at a group of strangers in a mall. We see this story in the news all the time.
I agree with those who advise that your DD get counseling to deal with this, so that she can understand that she is not to blame, despite what irrational people might think.