Big Ro clearly has a great relationship with his parents. Through his eyes he can't see how this could happen. Those of us with more volatile relationships with our parents understand this although don't condone.
Mine was not perfect but I am very loving and live in the moment, we have all grown closer over time.
I know well that many have volatile relationships with their parents I don't question that. What I do question is the frame of mind that carried out the murder, to go from innocent to a madman and back to innocent, what was flooding through his being while hacking away?