Is there anything different about criminals who use a knife instead of a gun to commit violence?

That's what happened this morning at a high school outside Pittsburgh where a 16-year-old sophomore slashed 19 of his fellow students and an adult before being stopped by school officials.

The teen is in custody, and all of the victims are expected to survive, police and hospital officials said.

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But why a knife?

"Anytime somebody commits a murder or assault, either by choking, stabbing or making bodily contact, it always speaks to a level of rage and perhaps a personal connection to the victim that shooting with a gun does not," said Naftali Berrill, a forensic psychologist in New York City.

"When you are stabbing someone, it's close and in your face. The experience is more visceral and more graphic, more provocative. It speaks emotionality, whether rage or paranoia."

Perhaps the student couldn’t get a gun, the weapon of choice for perpetrators of mass violence at schools, workplaces, malls and even military installations. Or perhaps he was living out a fantasy, Berrill said.

In some cultures, attacking multiple strangers with a knife is part of a mental disorder or syndrome called "amok," a term that originated in Indonesia, according to James Clark, a psychologist in Rochester, N.Y.

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Amok is a dissociative episode that begins with brooding, followed by a period of violence or homicidal behavior directed at people and objects, according to a psychologists guidebook known as the Diagnostic and Statistical Manual of Mental Disorders, or DSM-4. “It is initiated with a perceived slight or insult, and usually happens only among males.

The original reports of amok come from Malaysia, Laos, Phillipines, Papa New Guinea, Puerto Rico and the Navajo.

"It's not a great leap to suspect that this occurs in American populations as well," Clark said. "But it's probably more impulsive and limited by what's available. We all have kitchen knives at home."

Other experts say that more important is the planning that went into the event, rather than the choice of a weapon. People who study violence put perpetrators in two categories, predatory or reactive.

The predatory aggressors are "scarier, they are the ones that keep up us at night," said Kimberly Gorgens, assistant professor of psychology at the University of Denver and a neuropsychologist in private practice.

Gorgens said that a major incident of random stabbing occurred recently in China.

"Who is to say that this China stabbing wasn't romanticized in this kid's mind to be a viable option for someone who couldn't put his hands on a gun," Gorgens said. "Or put him in a history book as someone who was interesting or notorious."

Gorgens, Clark and the other psychologists say that little research has been done in the differences in murders or criminals who use knives versus guns.

"People are going to be looking at what's available at the moment," Davis said. "If someone had a choice between semiautomatic weapon and butcher knife. I'd like to ask them why did you chose that. I would get a personal response related to the situation rather than something that describes the attitude of the perpetrator."