From Bruce Bower at Science News:
A dearth of research means the science of rampage shootings simply doesn’t exist…
Nor does any published evidence support claims that being a bully or a victim of bullying, or watching violent video games and movies, leads to mass public shootings, Winegard contends. Bullying affects a disturbingly high proportion of youngsters and has been linked to later anxiety and depression (SN: 5/30/15, p. 12) but not to later violence. In laboratory studies, youngsters who play violent computer games or watch violent videos generally don’t become more aggressive or violent in experimental situations. Investigators have found that some school shooters, including the Newtown perpetrator, preferred playing nonviolent video games, Winegard says.
Still, a small but tragic group of kids lead lives that somehow turn them into killers of classmates or random strangers (SN: 5/27/06, p. 328). If some precise mix of, say, early brain damage, social ineptitude, paranoia and fury over life’s unfair twists cooks up mass killers, scientists don’t know the toxic recipe. And it won’t be easy to come up with one given the small number of mass public shooters to study. More.
The main problem here is precisely as noted by Bower: “the small number of mass public shooters to study,” who live scattered over large regions. For example, suppose three out of sample of ten shooters are one of a set of identical twins, or left-handed, or adopted. A great deal of socially useless or harmful nonsense could be generated on those subjects because they are already subjects of research interest. But in the larger sample that we are thankful not to have, that bias would likely be engulfed.
A couple of other thoughts: Many parts of the world are more violent than, say, North America or Western Europe. Mass shooters are considered a huge public problem in Canada. But elsewhere, in the midst of a civil war or ethnic cleansing they might not even stand out. We don’t know because we have no generalized sample of the human race.
Law enforcement personnel are much more numerous than mass shooters and typically have a more normal psychological profile. Why not then invest more research money in studying 1) remedies for the problem that nothing is done about a clear and present danger and 2) why so many interventions go so wrong? – O’Leary for News
See also: Was Anders Breivik not insane?