What Were They Thinking?

February 15, 2008 — -- School shootings like the one at Northern Illinois University are usually linked to a mental disorder of the gunman, whose anger, social isolation or desire for attention bursts into violence, experts told the ABC News Law & Justice Unit.

Some of those experts recommend that schools make mental health a criterion for admissions, while others say steps as simple as locking classroom doors go a long way toward safer schools. And while media coverage no doubt prompts some "copycat" incidents, the experts say news coverage also provides important information that can make prevention possible.

Why Do School Shootings Happen?

A mental health problem is often involved, experts said. The NIU gunman, for example, reportedly stopped taking medication for an unspecified disorder and was allegedly behaving erratically in recent weeks. An inordinate drive for attention can lead shooters to create a spectacle, to copy incidents like the Virginia Tech shooting, which drew enormous publicity, says Katherine Newman, a professor at Princeton University. Randomly shooting strangers is more about crafting a dangerous image than about the victims, she said.

The most recent shootings have generally occurred on college campuses because shooters in college are older and their mental disorders are further along, Newman said. Colllege age shooters are less constrained by the rules and social structure of high school and college campuses are physically more open and harder to monitor, she told ABC News.

The Columbine High School massacre in 1999 was a watershed moment, said Ron Stephens of the National School Safety Center. It provoked copycat shootings and illustrated the possibilities of directing deadly violence at not just at an individual, but indiscriminate targets.

How Can They Be Prevented?

Stephens recommended that colleges and selective high schools evaluate students on their mental health as well as their academic and athletic talent. He acknowledged the legal obstacles to doing so —