That's another thing, it does boil down to parenting, but in this case... not really.
I could see if a kid smoked at 15 and society begged the question "How did this happen?" Well, if the parents smoked, then probably because the parent didn't teach the kid the proper dangers of cigarettes..
But killing... at 17, regardless of what parenting you had, you know damn well that killing is wrong. You KNOW damn well not to imitate things you see on tv. It's not like a natural instinct to see animated cartoon violence and then turn around with a conscious mind and make the choice to act that violence out on another person.
Looking at it from another point of view, people are always quick to blame the parents when in reality, the kid could've had perfectly normal parents and just made a stupid decision.
In response to a post above asking his method of killing, he used a hammer:
http://www.cnn.com/2004/WORLD/europe...hunt.storeban/