Pretty much everything you've been told about mass murder is wrong. GTA and other video games don't make them happen, and the perps don't just suddenly snap and go berserk: they plan these things fairly meticulously, which is why L'il Jimmy Holmes bypassed at least half a dozen theaters, many of which were closer to his residence, and instead selected the one theater that made a point of publicizing its "gun-free" policy.
The article Mass Shootings in America: Moving Beyond Newtown examines policy proposals to avert killing sprees, and argues that their prospects for reducing the risk of murderous rampages are limited.
As well, despite widespread reporting leading many to believe otherwise, mass shootings are not on the rise, and the so-called "assault weapons" ban of 1984-1994 had zero effect. Nor do "enhanced background checks", as mass murderers generally have no criminal record or known mental issues - and so they can easily pass such checks.
Oh, and after every shooting, pundits rush to ask why no one saw the warning signs. This plays well in the media, and consumes airtime in ways that appear more meaningful than the story about the cute baby otter at the zoo, but that's about the extent of it. The fact of the matter is that there are no warning signs; the shooters are most often white guys, but that's as far as it goes. Sociopaths are extremely adept at blending in, being more or less invisible - and hiding their resentment over being ignored. There's no warning, no way to know beforehand what's coming; you just have to deal with it when it does come.