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:
- Recurrent themes of destruction, violence, hopelessness, hatred, loneliness or nihilism in a student's writing, artwork or conversation.
- Overwhelming feelings of rejection or humiliation after the end of a love relationship
- Low tolerance for frustration, poor coping skills and a lack of resiliency
- Refuses to take responsibility for his or her actions and typically blames other people, events or situations for any failings or shortcomings.
- Nurses resentment over real or perceived injustices
- Unpredictable, uncontrolled or out of proportion outbursts of anger
- Lack of empathy for feelings of others
- Access to weapons or explosives
- Turbulent parent-child relationship
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.