We've had threads on this before.
But no, I do not believe in the least that games, movies, etc. are responsible for people being violent. There can be some effect, but generally this is if the person is already pre-disposed to violence, cannot differentiate between fantasy and reality, or otherwise has issues. But really? Not a single credible study has shown any real link. Seriously, in just about every case where someone has tried to blame violent games or music or movies on someone going nuts, if you look at that person's background, it's pretty clear they weren't right in the head to begin with.
And Jack Thompson is a joke. I don't think anyone takes him seriously anymore because he always comes off as such an idiot. He generally has no idea what he's talking about, and if I remember correctly, he was suspended from practicing law and ordered to undergo a psychiatric evaluation. The guy is nuts.
It's all just scapegoating. People don't want to deal with personal responsibility, so they try and pin the blame on anything convenient that they can.