(Mr Pedantic can mark me later )
I fear we are getting into the Nature V Nurture argument with that statement.
I agree that his family cannot be held totally responsible for his actions. However, his upbringing and family circumstances must have had some bearing on the type of person he became.
I have no reason to doubt people who say his family are nice people. I, for one, don't hold them responsible for his actions. What I am saying is that upbringing and family circumstances do have some bearing on what sort of an adult a child becomes.
I suspect that this is probably not correct in the case of true psychopaths