Another thing...
Why would the shooters claim to be in league with the game manufacturers? My impression of those guys is that they want to be remembered as fearless hell-raisers who took a stand against a stifling, conformist society, not the hapless dupes of big business.
The closest you could probably get is some mass-shooter gets sent to prison, has a jailhouse conversion to Christianity, and then tries to "redeem" himself by claiming that he was manipulated into his killings by the video game industry(similar to David Berkowitz's later claims of satanic inspiration). But by that point, he's gonna have been out of the media spotlight for a while, and no one's gonna be paying much attention to what he says, just dismiss him as a crank.
I'll admit that your scenario is an intriguing one, might make a good movie.