There are tons of studies that indicate that consuming violent media results in violent behavior, there are roughly an equal number of studies that indicate the opposite.
When it is all said and done, if you compare crime rates over the last 30 or 40 years, we have seen a dramatic decline in violent crime since the advent of the FPS. You just can't reasonably argue with numbers like that. Go do some research for yourself. Look up the release date of Doom 3D and look up crime rates sorted by year. Those who say video games are the cause of violent crime just have no statistical leg to stand on.
Now if you compare crime rates now to crime rates before mass media, then you will notice that there was a significant increase when mass media hit. So lets blame radio, newspapers, and TV. But Video games statistically have correllated to a decrease so they should be the cure right?
The truth of the matter is that around the time mass media was inundating our society we really ramped up the moving into bigger and bigger cities and the bigger the cities got the less you knew your neighbors because there were just too many people to care about them all. This lead to a weaker support base for a would-be psychopath to help them live right and plenty of targets that they can easily dehumanize due to lack of familiarity, and as a result of that, they snap. You cannot develop a society as large as ours and hope to eliminate the possibility of every psychopath to go on a killing spree. Blame the psychopath, not the hobbies that the psychopath took pleasure in (unless it was torturing puppies and the like).
If a lunatic opened fire on a courthouse after a long successful day of fishing or playing golf, would we blame fishing or golf for the the attack? No! We would blame the lunatic. Why is it any different with video games? As the previous posters indicated, its the newest form of media and therefore the current boogeyman that idiots point to to assign blame. That is all.