I would suggest in fact that some of the signs this troubled individual would behave in this manner were probably already apparent to his parents, but they chose to dismiss it because no parent really believes their own child can be capable of such horrible behaviour.
This is a person that needs professional help - from an objective third party. The authorities, while certainly imperfect, can provide this.
For all you know, when this adult was confronted and "broke down" it could have all been an act. He could truly be a psychopath (and his actions certainly suggest that)