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.
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.