To be clear: I am not asking if violent video games cause violent behavior. That is covered here.
I am more interested if there is any correlation between violent video games and mass killings. I want to know if the killers are any more or less likely to play video games than other people from similar backgrounds. Video games are often a target for blame in these tragedies:
"At times like this, we need to take a comprehensive look at all the ways we can keep our kids safe. I have long expressed concern about the impact of the violent content our kids see and interact with every day," Rockefeller said in a statement. "As Chairman of the Senate Commerce Committee, I have introduced legislation to direct the National Academy of Sciences to investigate the impact of violent videogames and other content on children's well-being." --West Virginia Senator Jay Rockefeller
But from my own recollection it seems that there is no connection to video games more often than there is. Given the number of young males that play these games, it may even be an abnormally low number of these people who play violent video games.
It is well-known that the killers in the Columbine massacre were avid players of Doom. The shooter in the Sandy Hook Elementary shooting is said to have spent hours in his basement playing Call of Duty. The killer in the Virginia Tech massacre played some Counter-Strike, but probably not very much. The killer in the 2011 shooting in Norway said he trained for the attack by playing Call of Duty. I can't recall others.