Do you recall the case of the Austrian Fritzl? Even if we assume that your view of the world is correct, the idea that abuse victims (actual ones) who have been abused all their lives will act in a remotely rational way is doubtful. The only reason Fritzl was caught is because he sent someone who was wounded to the hospital instead of letting the kid die.

Yes, this seems like a very hard case. But given the amount of stuff that is alleged, if even a small portion is true, it would justify offing him in my mind. On the other hand, you don't want to give people the right to kill others based on unsubstantiated claims.