"I can't just pick up any Tom, Dick or Harry under the sun," Lanning said. "I'd get sued. The bottom line is this is what American society struggles with all the time, balancing public safety with freedom and rights."
The most iconic of all school shooters -- Harris and Klebold at Columbine and Cho at Virginia Tech -- could not have been more different, according to most experts.
Cho, 23, was mentally ill and delusional -- a psychotic, mental health experts have said. As early as 2005, two female students at Virginia Tech complained about the anxious son of Korean immigrants, and a state court declared him to be at risk for suicide, referring him for psychiatric treatment.
Like the Columbine killers, Cho took his own life in the rampage, but mental health experts have said he may have suffered from bipolar depression or schizophrenia
Unlike Cho, Harris was a psychopath -- controlling, manipulative and sadistic, according to journalists, psychologists and law enforcement experts who studied the case. Psychopaths are in touch with reality and rational, and nearly always well-liked and charming, according to experts.
Klebold was a lonely depressive, full of mood swings and suppressed emotional rage, according to psychiatrists involved in the case.
But together, the Columbine pair was a "deadly dyad," according to Dave Cullen, a journalist who has covered the tragedy a decade and published a book, "Columbine," this month to coincide with the 10th anniversary.
Neither the Chos, nor the Columbine families ever talked freely with the press about their sons' actions. But in 2004, on the fifth anniversary of the tragedy, Tom and Sue Klebold, who still live in Littleton, Colo., responded to an article in the New York Times.
The Klebolds told reporter David Brooks that they objected to the way their son had been described as "depressive" and blamed the toxic atmosphere of teasing at the high school.
But Cullen said that unlike Cho, who was not well-liked and kept to himself, Harris and Klebold had an active social life and were bullies, rather than bullied.
"We always get the wrong answer because we phrase the question wrong," Cullen said.
"Everyone says, 'Why did they do it?' That gets you in trouble. There isn't one thing to explain Columbine," he said. "Why Eric did it and why Dylan did it -- they are polar opposites. You can't fuse it into one.
"It's the same thing with school shooters," he said. "We still go the same route and look for a profile and think we've got one -- outcast, loners and bullies. In two-thirds of cases, they don't apply. There are three or four or five profiles."
According to former FBI psychiatrist Frank Ochberg, who worked in hostage negotiations in the 1970s, Cullen's book "hit the nail on the head."
"The general public has its own idea about evil and how it gets created, distilled and powered," Ochberg told ABCNews.com. "We have so many archtypes."
Harris was a "budding psychopath, a person without a conscience," he said. "He got his satisfaction by dominating."
"Psychopaths don't feel guilty because they are blind to guilt," Ochberg said. Harris also had sadistic tendencies, which propelled him to "seek vengeance."
Klebold, on the other hand, was depressed, with pent up anger and "mood regulation problems," but together, they had "violent creativity," Ochberg said.