A recent analysis of spree killings in the US concluded that approx 90% of all the documented US spree killers committed their acts whilst the balance of their mind was disturbed.
Someones state of mind is far more relevant than availability of weapons or what TV show, film or video game they have been watching or have played.
The UK has a much stricter regulatory environment than the US, guns are much more difficult to acquire, especially assault rifles etc , but we have had our own tragedies - Hungerford, Dunblane, Cumbria.
Despite this observation, I do believe that civilians should be restricted as to what weapons they have access to. Assault rifles with a high rate of fire and large magazines have no place in a home, nor do pump action shotguns or automatic pistols. But in the US it will be a sisyphean task, given the sacrament that is the second amendment, and the fact that there are already an estimated 300 million guns in circulation.
I also think that we,as a public wanting to be entertained, and the entertainment industry, ought to re-examine what we class as entertainment. For decades we have enjoyed shows that depict violence as an acceptable solution. The immediate and long term consequences of killing are rarely shown. Heroes get a 30 second advertising break, then they are back in full swing, despite participation in brawls and sustaining injuries that would incapacitate for hours, days or even longer in the real world. Violent solutions are often justified, even the most desirable solution. Women are often portrayed as victims of violence. Video gamers get additional life, or can replay from their last save.
It is difficult not to conclude that all this exposure to such casual and consequence free behaviour does not have some effect on our sensibilities, dulling and coarsening our response to acts of mayhem and violence carried out in the real world.The entertainment industry often claim, with some justifcation, that all they do is hold a mirror up to society - but maybe we should hold up a mirror that offers us more enlightened behaviour?