I'll just add that it's more likely video games are actually decreasing real life violence cause it give some people a way to express some urges (basically like pornography, sports, arts etc).
And if some people can't tell the difference between violence in real life and violence in video games, it's not because of the video games themself, it's an educationnal issue (so blame the parents, the schools, the society, or the agressive one himself, whatever, but not the video game).