PHOENIX -- It can seem all but impossible to understand why anyone would commit a mass murder as Jared Loughner did near Tucson last year, as James Holmes is accused of doing in Aurora, Colo., last month, as Wade Michael Page did at a Sikh temple in Wisconsin last Sunday, and as happens, on a smaller scale, about 20 times a year in the United States.
Often, the specific "why" for a murderous rampage stays hidden within the twisted delusions or obscure psychosis of a particular killer. But forensic psychologists and other behavioral scientists are increasingly identifying reasons that can predispose someone to commit mass violence, and "warning behaviors," such as a fast-growing fascination with weapons and violence, that should signal the need for intervention.
"We'll never be able to predict which individual, out of many, will carry out an act of targeted violence," says J. Reid Meloy, a forensic psychologist and professor of clinical psychiatry at the University of California-San Diego.
But, Meloy said, it's often possible to identify people who fall into high-risk groups and to take some action to intervene -- from requiring counseling to restricting someone's access to weapons to seeking involuntary commitment, or many other steps in between.
"These strategies are being applied all over the country every day now, by mental-health professionals, teams in corporate settings and universities, by law-enforcement officers," he said. While he declined to offer specific examples, citing privacy concerns, he said there are many cases where the risk is being reduced, though it's impossible to say whether an act of violence is actually being stopped.
After Seung-Hui Cho killed 32 people and shot 17 others at Virginia Tech in April 2007, Virginia began requiring all universities across the state to create threat-assessment teams, groups including security or law enforcement, psychologists, counselors and administrators. The teams identify when an individual could pose a risk and consider how to respond. Many large corporations also have established threat-assessment teams or policies.
Intervening often isn't simple or easy. People in schools or workplaces may report worrisome behavior, but the information may not get to the right authorities, or they may not take what, in retrospect, may seem like the right steps. Or there may be other limitations.
Before the Virginia Tech shooting, Cho had been identified as stalking women and setting a fire in a dorm, both potential "warning behaviors" of further danger, said clinical psychologist and attorney Brian Russell of Lawrence, Kan. Cho was taken to a mental-health agency, but was ultimately sent for voluntary outpatient mental-health treatment.
"He checks in, he immediately checks out, and gets guns he couldn't have gotten with a court order for inpatient mental treatment or a judicial commitment," said Russell.
Loughner, who pleaded guilty Tuesday to killing six people and wounding 13, including then-Rep. Gabrielle Giffords last year, had been suspended from Pima Community College after a series of run-ins with police and college administrators. Three months before his attack outside a Tucson-area Safeway, police delivered a letter to his parents' home, saying he couldn't return to college until a mental-health professional confirmed that he didn't pose a danger to himself or others.
"The problem is that most people who are seriously mentally ill aren't going to do anything violent, and our ability to predict dangerous behavior is not that great," said Richard Cooter, an associate professor of forensic psychology at George Washington University in Washington, D.C. "If you tried to commit everybody who said something odd or weird or pick your term, you'd be locking up a lot of people."
In trying to understand what leads someone to commit mass murder, forensic psychologists sometimes focus on specific behaviors that show a growing or accelerating risk of violence. They also analyze the psychiatric and personality traits common to different types of mass killers.
Politically motivated terrorism aside, most mass murderers fall into one of three broad categories, many researchers say:
Those exhibiting psychopathic behavior. "At the core of the psychopath is always a profoundly malignant narcissism," said Russell. "They focus on what they need, and feel an entitlement to get what they need at the cost of anything to anyone else."
Those who are delusional. They maintain a persistent, irrational belief in the face of contrary facts, said forensic psychologist David Bernstein of New York City. "Those beliefs become their reality. There's an arrogance involved," he said.
Those who are severely depressed and suicidal. Loughner can be included in this category. It took more than a year of treating his illness with medications and therapy before U.S. District Court Judge Larry Burns ruled Loughner mentally competent last week, clearing the way for him to plead guilty.
Adolescent mass killers differ from adult mass murderers in some ways. One study, in 2000, found that adolescents are more likely to collaborate with others, are more likely to reveal clues -- Facebook postings, for example -- that they are planning something, and are less likely than adult killers to commit suicide.
Among the traits that many mass murderers -- adolescent or adult -- share are anger and a delusional sense of self-justification.
"Most of us learn to let things go, to see when something happens that it's not that big a deal in the scheme of things," Bernstein said. "These people focus and ruminate on their perceived wrongs; it becomes all-consuming. They feel they're correcting an injustice -- they're not the monster, the other people are the monsters."
Speaking of Page, the Sikh temple killer, Cooter, who stressed that he doesn't have personal, direct knowledge of the case, said that "from what I can tell, he wasn't psychotic; he was just an angry guy."
Some "warning behaviors" seem obvious, like a growing fascination with weapons, a focus on violent fantasies or previous mass killers, and expressed threats that may be subtle or direct.
A Secret Service study in 2002 found that in 81 percent of school-shooting cases, at least one person knew about the plans in advance; and in 93 percent, people around the attackers noted disturbing behaviors ahead of time, such as acquiring guns or writing poems or essays on homicidal themes.
A study last year said most adult mass killers, too, signal their intent in some way, though not to their actual target.
Often, too, there's what psychologists call an "energy burst warning," a sudden jump in activities relating to the target.
As the 2011 study notes, "Warning behaviors can only constitute warnings if the behaviors are detected."
Conceding that mental-health care options in many places are limited and inadequate, Meloy, who calls himself an optimist, makes two observations.
One: for all of the media attention to mass killings, the 20 incidents a year that occur on average means they remain exceedingly rare in a country of more than 311 million people.
The second: "After 9/11, New York came up with a catchy phrase, 'See something, say something.' If you're going to maintain a safe community and social fabric, and if someone is behaving in ways that concern you, you have to say something," Meloy said. "And I think, increasingly, people are willing to do that."