Experts say there are warning signs that a student or young adult might be prone to committing a violent act.
But they caution that youths who exhibit some or even many of those behaviors and attitudes are not necessarily destined to become violent.
What is crucial for parents, friends, teachers and others is to detect changes in behavior and to intervene before harm occurs.
"You have to strike a balance on warnings. Most incidents of school violence are one-on-one incidents between students, (and) that those type of things are much more likely to occur than mass shootings. You want to act on reasonable suspicions and good information, but you don't want to prompt confusion and panic,'' said Mo Canady, executive director of the National Association of School Resource Officers.
According to Ken Trump, president of the National School Safety and Security Services consulting firm; the FBI's National Center for the Analysis of Violent Crime, and others, here are some indicators to look out for:
Most important, said Katherine Newman, a sociologist at Johns Hopkins University who coauthored the 2004 book "Rampage: The Social Roots of School Shootings," is to be alert for specifics.
"I think the most important thing to realize is that the more specific a rumor or threat is, the more seriously it needs to be taken. It's one thing to say, 'I could just kill that guy', as a metaphor, and another to say "I'll be at school on Monday with guns,' '' Newman said.
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