The only people at fault are the other members of society who know about his behavior and won't take the necessary action to deal with him. Of course, the soft-minded will say life is never black and white, it's always varying shades of gray. If she stays with him he might get better. If she leaves him he might kill her. This is a complicated situation and we shouldn't second-guess her.
Life is black and white.
People who break the law are asking to be punished. That society fails to punish them is our fault, not the lawbreaker's. People who use violence in intimate relationships are capable of murder. This guy needs punishment and treatment. And, at this late date, even that may not be enough to save the lives of C. Mann and her children.