I'm not sure the parents are the only ones to blame.
He's got a sister who never thought of doing anything like that. The Marocco-frenchman Zacarias Moussaoui has an older brother who turned all right and completely condemns what he did. My own brother has not the same viewpoints as I have on many issues, but we have the same parents, thus were brought up the same way.
On the other hand, there is more and more violence by younger and younger persons. The parents don't spend as much time with their children as it used to be the case.
Also the notion of freedom is a fascinating one. Why leave a free society for one that has so many rules?
We all need guidance, we all need rules but their meaning is not the same from person to person.

Maybe an attachment to "values" is more important for some, when they haven't exercized their judgment with their critical spirit to evaluate what is good for them.
(To my horror, I read the notion of critical spirit has been completely twisted compared to what I learned at school and the university, (at least in the US).

Raoul