"When you have someone already on the edge, already looking for a way to express their anger, their frustration, that person ... can be tipped to action," said Dewey Cornell, a University of Virginia education professor and psychologist who has studied violence in schools.
"One thing that people have learned is that if you go into a school, you're going to get an incredible amount of attention - more so than if you go into a department store or bank," he said.
"There's something very gripping about a school shooting."
There appear to have been two distinct instances of copycat school violence in recent weeks. The first was on Sept. 13 when a tall, thin man wearing a trench coat walked into a college cafeteria in Montreal and fired shots. One person was killed and 19 people were injured.
That incident appeared to mimic the 1999 Columbine High School shooting in Littleton, Colo., in which both student attackers wore trench coats and fired at classmates in the cafeteria. A total of 15 people died.
Five days laterThen yesterday, police say, a 32-year-old milk-truck driver walked into an Amish schoolhouse in Lancaster County, Pa., and acted out a terrifying scene remarkably similar to one at Platte Canyon High School in Bailey, Colo., just five days earlier.
In both cases, a suicidal gunman entered a classroom, released the boys and lined up the girls against a blackboard before shooting at them. And the shootings were committed by adults, not students.
"I think copycatting is a huge issue," said Dave Cullen, author of a book on the Columbine massacre. It is "beyond the realm of possibility," Cullen believes, that yesterday's shooter wasn't aware of the details of last week's attack.
The common denominator in many school-violence attacks is probably a desperate bid for attention, experts said.
"This is a way of achieving instant fame," said Kirk Heilbrun, a Drexel University psychologist, "the easiest way to get yourself out there, your face on the cover of a national magazine or newspaper."
But the mere desire for attention doesn't fully explain such sensational violence, said Cornell.
"Attention is part of it, attraction to notoriety, but [also] the suggestive power of the event and some desire to share in that kind of event or to be a part of that," he said.
"It's not a very rational process. It's not a logical process. We're dealing with people who are not in a rational state of mind."
Minutes before yesterday's shooting, Charles Carl Roberts IV reportedly called his wife from the Amish schoolhouse to say that he was exacting revenge for something that happened to him 20 years ago.
No specific targetCullen, who has conducted extensive interviews with psychologists investigating Columbine, doesn't believe revenge for a specific event was the shooter's true motivation. More likely, Cullen said, he was deeply angry at the world.
If Roberts were seeking to get back at someone, Cullen said, he would probably take a gun and find that individual.
"He is only going to open fire indiscriminately if he doesn't have a target for that rage," he said.
Experts emphasized yesterday that a mind capable of such indiscriminate violence is exceedingly rare, and they cautioned against stoking public fears - particularly because attention is a prime motivator in such crimes.
"I am very concerned that these cases don't generate media attention that stimulates more angry and deranged people to take similar violent actions," said Cornell.
Children are still safer in school than they are anywhere else, including their homes, he said.