The Anatomy of Violence

Rates of criminal violence are higher in mobile and heterogeneous societies where it is hard to put down roots and establish the social glue that binds people into a community. The United States, of course, is a highly mobile society and, as a result, a nation of strangers. Murder and violence are also higher in nations with the largest income inequality. The United States ranks high on this problematic measure. Perhaps it was no coincidence that Cho railed that "your Mercedes wasn't enough, you brats. Your golden necklaces weren't enough, you snobs. Your trust fund wasn't enough."

As long ago as Tocqueville, observers have divined that the American character had been forged on the frontier. Far from civilization and the reach of laws, we created the cult of the rugged individual who took justice into his own hands. While it's tricky to argue that the "American character" explains a murder spree by a Korean immigrant, living here for 15 impressionable years, Cho could not have avoided soaking in the competitive, individualistic aspects of American culture. "In this country more than others, we admire winners and we blame people for their own inadequacies," says Fox. "Mass murderers tend to be losers, people with a history of failure. The feeling of worthlessness gets internalized" in the barrage of messages that an individual's fate lies entirely in his own hands—something Asian countries view as ludicrous. If success by the usual definition proves elusive, there is another path. The Columbine shooters wrote in their diaries that they needed a certain body count to reach "movie status." In this media-soaked culture, for Hollywood—or even the most demeaning reality show—to care about your story is the ultimate validation.

The cult of the individual finds its ultimate expression in, yes, America's gun culture. "Guns are the ultimate way of being self-contained and powerful," says Sheras. No matter how the world has treated a potential killer, "if he has a gun he can automatically feel equal to everybody else."

Individualism exacerbates the sense of injustice that the aggrieved feel, something alien in low-violence countries. In Japan, people are taught to endure hardships, small and large, from early childhood. It is even part of the language: gamanshite roughly means "endure it." Japanese say it and are told it all the time. If they do feel angry or frustrated, "we would rather endure it and kill ourselves than kill others," says Masakazu Suzuki, a theologian and teacher in Tokyo who attended college in the United States. "We don't choose mass shooting for a public revenge, but just kill ourselves, perhaps with a note expressing anger toward those who oppressed us." Suicide rates in the Far East are nearly six times the homicide rate.

No discussion of violence in American culture is complete without mentioning blood-soaked videogames. Right after earning points for a graphic disemboweling, young players are more aggressive, but more in punch-little-sister mode than shooting up a mall. Still, there is evidence that violent games have a numbing effect. "When people stop feeling it's terrible that someone is getting hurt, that's dangerous," says Pollack.

And so the blocks stack up one by one—the biology that mass murderers carry from birth, the brain circuits laid down as they experience life, the messages they soak up from the world around them. No single experience or character trait is sufficient, no single one to blame. But even as science identifies the forces that sculpt the mind of a mass killer, explanation is neither excuse nor exculpation. Somewhere in all this is the will, the decision by the gunman to pull the trigger. Understanding that is the greatest challenge of all.