The risk factors that are linked to these events — basically, being an angry young man — are so widespread in the population, he explained, and so weakly predictive of an individual actually committing a mass shooting as to be practically useless. “The answer is yes, at least of the most highly publicized, most fear-inducing cases of stranger shootings, by and large they are angry young men,” said Appelbaum. “But that doesn’t get you very far, because there are a lot of angry young men who are angry for all kinds of reasons, and unless one wants to lock them all up or put them all under 24-hour surveillance, it’s really impossible to build on a description that general to come up with effective preventative approaches.”

Once you move past that incredibly broad category, he explained, “you’re really into murky territory where you’re identifying categories that some people fall into and others don’t,” he said. Take mental illness: While more and better-funded treatment for mental illness is obviously a good thing, Appelbaum said it just doesn’t have much of a direct connection to mass shootings. Sometimes mass shooters have a history of mental illness, but “[l]ots of people who commit mass killings are not mentally ill in any classical way,” Appelbaum said, noting that he wished Obama hadn’t mentioned mental illness in his address last night.