Did video games have an effect? Sure! So did what he had for breakfast, the composition of oxygen in the air, his chemical state based on vitamin intake, the background noise of the evironment, and the bubbling and twisting of the quantum foam at the base of the universe.
The key is, which environmental effect had the MOST effect? In most cases: parents.
Y'all know I live in Texas. Out here we love our guns. But in many cases, kids learn of guns from their parents, who teach them to respect their firearm. Don't point it at something unless you plan on shooting it. Don't shoot it unless you plan on killing it. Ergo, don't play with the darn thing unless you're planning on using it to kill, and what you kill darn tootin' better have been trying to kill you or avoid you eating it!
In Dallas, the owner of a firing range kinda looked at me weird when I asked if they did training. The "shouldn't you have learned that from your Dad?" (Note: Dad and Mom are both California Hippies

). The gun shop owner down here locally seemed surprised as well.
Here's the problem with firearms: In many places, they're feared. And the population plays ostridge: if I don't know about guns, guns won't know about me! They try to hide their guns from other people. And if you get somebody who uses their constitutional right to bear arms, and worse, uses their state protected right to carry the firearm in public... MUST BE A MASS MURDERER.
In a local city, Tyler, a crazy man got his hands on a gun and went to city hall a while back and started shooting people. The police were unable to get on the scene quick enough to stop the carnage. A regular citizen, with a Concealed Carry Permit and training on his firearm, pulled his gun and shot the gunman dead. Saved many lives. The police checked up to make sure the weapon wasn't used in a bad way, and the guy walked away. He had learned how to use his gun with respect.
But in most places, this training is never given. Kids don't learn about gun safety and respect until they've done gone to a school and opened fire.
So who's fault is it?
Gunmakers for providing the gun? 5%
Hip hop artists that make guns sound fun? 5%
FPS games that make miniguns funny? 5%
Parents who allow their son to have a gun? 40%
Parents who never teach their son to respect his weapon? 45%
Sure, everything has a little effect. But the main problem is parents expecting schools to raise their children, then getting shocked when their kids do something like this.