I'm about to simultaneously argue against everyone here.
First of all, man is born helpless upon the world and it is only through the ingenious evolution of weapons that we have survived as a species. Your (anyone's) argument that guns should be banned or further limited is ridiculous and speculative. If you did alittle research, you'd see that your initial reaction is incorrect; restrictions on guns cause more deaths than they prevent. Why? Bad guys know how to get guns whether you want them to or not, and guess what all those deadly cartels love to sell on black markets? Drugs and guns. Guess what would instantly shut down said deadly cartels? Legalizing all guns and drugs.
Lack of education is the culprit here, not the weapon. Whether you want to accept it or not, the boy could have found dozens of ways to kill his parents if he was crazy enough (and he was). Poison, easy-to-Google homemade explosives; It could have been anything. However, the stupid father/mother left the gun safe unlocked, so it was that. There is no argument against this fact.
The word you were looking for (whoever you are) is neurotransmitter.
Yes, addiction can happen, and you can get addicted to video games. Yes, the boy's motivation to kill was probably the addiction, although not necessarily so. We don't know exactly what was going on here. For all we know, the parents were abusive and the video games were the kid's only escape.
Regardless, like it's been said before, the kid was crazy, video games or no. To say that they boy didn't know his parents would be dead when he shot them is just...retarded. There is no other word for it. If this kid was 6 years old, yeah, okay. But look at him. He's at least 16. Teens and preteens know what death is and what happens when you get shot with a gun. Hell, they've seen it a million times over on the TV and in games. Guess what, when you shoot an alien in Halo, does it come back to life? NO. Argument rejected right there.
I also find the hypocrisy here alittle entertaining. If this was an adult, you'd all be screaming for blood and vengeance. Because the kid is young, you all (almost) believe he's fixable. Guess what? There is no evidence that teenagers are more prone to rehab than adults. If you want fairness and compassion, you must want it for EVERYONE, or you're just a lousy hypocrite.
TL;DR: Guns - not the culprit
Games - not the culprit
Crazy/Stupid - Always the culprit