How far do games such as manhunt and manhunt 2 provoke actual violence?

Throughout the internet I found hundreds of articles and a lot of them appear to be more biased towards the idea that video-games (in particular manhunt and manhunt 2) provoke violence among teenagers and that of younger ages. The interesting thing about these opinions is that not many of them show actual facts/figures backing up their arguments, and those that do feature links to news reports never officially state that the game itself was responsible.

They always state that the teen had a copy of the game in "his/her bedroom" and then upon further research of that particular case there is a lot more evidence backing up an alternate reason to do with the murderer robbing the victim in order to obtain money to feed his drug addiction.

However upon reading other articles and web pages across the internet is seems that articles disagreeing with these theories stating that video games encourage murder and violence, generally have more of a leg to stand on and generally have links and quotes made by top scientists who know a lot more on the subject than biased opinion based people.