It is not a simple as just yes or no.
While i highly doubt videogames alone can be The Cause of violence, there is a very weak effect similar to that generated by watching a relation from ongoing war. The safety glass shield protecting the viewer from everything thats going on the screen flattens the actual perception.
It's just something we watch, that will be interrupted with commercials, at every moment we can switch it off, change to other channel and because of that the impact of the incident itself is much much smaller than if we would actually be there.
Both games and movies that show violence are of course different form the actual war, but in a way it is still the same effect of taming something, we would see as terrible when experienced in person. Sometimes, under very specific circumstances mind might just get used to the sight of blood or force abuse so much it will treat more closer to norm than it should. For such thing to happen however, there needs to be some kind of underlaying cause, be it the social environment the person is often exposed to, mental disorder or personal, repetitive experience.