The Why Files (http://whyfiles.org) asked people who are paid to understand these crimes to take us inside the heads of juvenile mass murderers. Here's what we learned.
The recent bunch of accused killers are "very self-centered, very self-absorbed, angry youngsters who derive extraordinary pleasure from savage vengeance they wreak on one another," says Shawn Johnston, a psychologist in private practice in California. These descriptions, he adds, "are pretty consistent with what I've seen" during more than 5,000 interviews with juvenile and adult offenders in almost 20 years of forensic psychology.
The mental world of these young killers is "all about 'me'" Johnston says. "They're frustrated, angry, in some pain, not getting everything they want. They feel like victims. They have no concern about others -- they don't think about others. It's all about who they are and what they want."
Dorothy Lewis, professor of psychiatry at NYU School of Medicine, told a PBS Frontline documentary that pathological aggressiveness is rooted in abuse and pain. "Probably the most powerful generator of aggression in living beings is pain... Animals that have been tortured and children who have been severely and repeatedly abused often become extremely aggressive. Animals and humans being raised in the company of violent adults is associated with the development of aggressive behavior patterns."
Johnston agrees, saying that aggression has been called the "default" setting for human behavior. People turn aggressive, he says, "when you don't have the problem-solving means of talking, negotiating, when you can't get what you want."