This is the second in a series on Columbine, 10 Years Later
Two years ago today, Seung-Hui Cho slaughtered 32 students at Virginia Tech, claiming to have been inspired by the two teenagers who carried out the Columbine shootings, calling them "martyrs" in delusional diatribe he videotaped for the world.
"You had a hundred billion ways to have avoided today," he said on video aired on national television. "But you decided to spill my blood. You forced me into a corner and gave me only one option. Now you have blood on your hands that will never wash off."
In 1999, when Eric Harris seduced his friend Dylan Klebold to open fire at Colorado's Columbine High School, killing 13 and injuring 24, no one had a definitive profile of the school shooter.
Today -- as the 10th anniversary of the Columbine tragedy on April 20 approaches-- experts say they can't predict which teens will go on a suicide-driven rampage..
"Not all psychotics or psychopaths are going to kill and most are not dangerous," said veteran FBI behavioral scientist Kenneth V. Lanning.
In 2000, The National Institute of Justice joined forces with the Secret Service and the Department of Education to assess ways to prevent school shootings.
Looking at 37 school shootings to find patterns in school-aged assassins, the study concluded that all are male and most are loners, with some kind of grievance. More than half had revenge as a motive.
"But that's typical of almost every adolescent," Lanning told ABCNews.com.
"The biggest problem with school shooters is the false positives and false negatives," he said. "How many people in any school have all these characteristics and will never shoot anybody."
Reports from the Department of Education show schools to be largely safe. But high-profile shootings have caused anxiety among parents, students and their teachers.
Contrary to public perception, school shootings declined after 1993, although there were copycat incidents from 1997 to 1999 "stimulated" by unprecedented media coverage, according to the National School Safety Center.
Still, they continue to capture the nation's imagination with images of vengeful outcasts, trench coats and bullied loners.
Some of the conclusions of the federal report were borne out in the Virginia Tech tragedy: shooters tend not to snap, but usually plan months or years in advance and often tell a friend or classmate.
Cho reportedly began planning his attack more than a month before the 2007 massacre, when he purchased his first gun. His video, made in combat gear, appears to have been made at least six days before the attack.
Harris and Klebold also planned in advance, with journals and "basement tapes" chronicling their plan to blow up Columbine High School.
But the comparisons end there.
And when the public throws around words interchangeably -- like psychotic and psychopath -- they underscore the need for better mental health education.
"When we see a person go off the deep end in a shooting, we look in hindsight and piece it together," Lanning said. "Frequently all the warning signs were there and we should have known. But you get warning signs one and two from the mother, three and four from the teacher, five and six from the counselor and probation officer."
Schools need to find better ways to accumulate information and share, within the boundaries of privacy.