Blaming video games for shootings

We all of course have heard the horror that has unfolded in the last 24 hours, and I'm sure that we all can condemn and give our condolences to the families.

(Unrelated, but no one else seems to know about the 22 kids which were stabbed in China)

But that is not why I am posting.

Video Games, shooters, more specifically, are being blamed for any source of violence in western world. Call of Duty was blamed for Oslo, Colorado and (Mistakenly) Mass Effect in the more recent Connecticut shooting.

So I ask you, do violent video games contribute to real violence? Or, It is cause or causality?

Discuss.

(For both sides of the argument, this website has some great information)