After the shooting at Sandy Hook elementary many people began looking for someone, or something, to blame (most likely because the killer (and I will not mention his name in this article) took his own life and the public wants some sort of sense of justice) and there are a lot of things they are blaming.
While the main focus of "blame" is on gun control laws and improving mental health care, people are also focusing their blame on videos games (just like they did after the Columbine massacre).
The particular is on violent video games, and while the killer did play video games in high school, it's not clear if he played video games into his adulthood, nor is it known if he played violent video games.
Even if the killer did play violent video games for hours on end, it doesn't mean that it caused the killer to take his mother's guns, go to a nearby school, and murder a bunch of kids and teachers. He probably would have done it anyways regardless of if he never watched any type of violent media what so ever.
If video games caused young people to become violent killers, then there would be more school shootings then there really are (and by the way, the media does tend to sensationalize this stuff. School shootings are actually very rare) because lots of teenagers play violent video games. In fact I played violent video games with my friends when I was a teenager, and it never made any of us violent. If anything those games kept us from going out and getting into trouble.
Video games do not cause people to become violent. What causes people to become violent is either long term exposure to real violence (not imaginary violence), psychological issues, drug addiction, or a combination of two or all three.
The reality is that video games (and also music, movie, and television, which are also some things that some people are claiming influenced the killer to do what he did) do not cause people to become violent, and there is no evidence that it does, and by all appearances this is nothing more then a moral panic by people who think that seeing fictional violence will cause kids to commit real violence, much like how some people back in the 1980's believed that playing Dungeons & Dragons would cause teenagers to convert to paganism and Satanism, or that reading Harry Potter would cause kids to start practicing witchcraft.
No video game in the world, no matter how violent it is, is going to influence someone to go out and kill a bunch of people, the same as keeping kid away from any exposure to violence is going to keep them from becoming a psychopath that kills a bunch of people.
One more note: Most video games are violent, be it either cartoonish, or realistic. Heck, the first video game I ever played, Super Mario Bros, would be considered violent, but it never caused to want to go and jump on top of people's heads and throw fire balls at them. If any negative things happened to me from playing video games then it would be that I would sometimes play them for hours on end (much like many people do today).