On August 30, 2006, a 19-year-old youth, clad in a trench coat, drove into the parking lot of his former high school in Hillsborough, N.C.--and began firing. Eight random shots wounded two students. When the police arrived, Alvaro Castillo gave up without a struggle. It was Castillo's second exploit involving firearms that day. Earlier Castillo had murdered his father in the family home.

Three months later in the small town of Emsdetten, Germany, 18-year-old Sebastian Bosse posted a video message on the Internet: "I can't f–kin' wait until I can shoot every mother-f–kin' last one of you." He then drove to his former school, armed with out-of-date rifles and homemade pipe bombs. Marching through the building, he shot randomly at students and teachers, injuring 37 people before ending his own life.

And the deadliest school rampage so far occurred on April 16, when a 23-year-old college student named Seung-Hui Cho killed 32 people and wounded 25 others on the Virginia Tech campus in Blacksburg. After police arrived, Cho put a gun to his temple and pulled the trigger.

The overall number of homicides committed at U.S. schools has declined since the 1990s--a trend that jibes with the declining rate of homicides carried out by juveniles across the globe. Yet some of these killings now display a new quality: they are premeditated and choreographed, down to the weapons used and the clothes worn. My colleagues and I have detected a sharp jump over the past decade in the number of such school shootings worldwide--excluding gang-related incidents--that were intended to kill at least two people or a school official. In the U.S., the rate of such extreme killings has declined only slightly in the past four years from an uptick in the late 1990s. Incidentally, the vast majority of the perpetrators are male; by our count, females instigated only four of the 101 school shootings that have occurred worldwide since 1974.

The chances of dying at school remain exceedingly small [see box on opposite page], but the most recent spate of school shootings has cast a dark shadow over a place intended to be a safe, enriching environment for children. This terrifying trend has brought a new urgency to efforts to unravel the roots of such deviance and to help educators, parents and psychologists recognize signs of trouble before a problem escalates.

About two years ago my colleagues and I co-founded the Institute for Violence Prevention and Applied Criminology in Berlin in part to design guidelines for preventing violence in schools. Since then, our work with violent adolescents and adults has helped us understand some of the motivations of young shooters and identify several warning signals that can help predict school rampages.

Many of our insights have come from analyzing the violent fantasies of adolescent shooters. These imaginings take root in a desperate mind that yearns for recognition. Often these young assassins are inspired by examples set by previous shooters. The fantasies typically intensify over a number of years before they are acted on. With time, the mental images become more detailed, and they often become buttressed by a distorted sense of what is just or moral, such as the need to avenge a perceived offense or the belief in a divine right to decide the fate of others.

Early on, troubled teenagers typically keep these fantasies secret, but they increasingly begin to leak their thoughts and plans to friends, chat rooms and even media outlets. Recognizing the signs of such deadly thoughts, as opposed to harmless daydreaming, can enable parents, teachers, social workers and other trusted adults to head off trouble before it begins. We have recently developed strategies for identifying youths at risk, for helping to prevent them from descending into a destructive fantasy world and for reacting expediently in the event of an imminent or actual shooting [see box on page 57].

Seeds of Violence

Fantasies and dreams often stimulate productive human activity. They also drive the healthy psychological development of children and adolescents, making possible prospective, or "wishful," thinking and creativity. So it is normal for an adolescent boy to escape into reveries about lovemaking with his girlfriend during an acutely boring class in school.

Of course, dreams and daydreams sometimes have a dark and violent cast to them. Almost everyone has imagined vengeful scenarios, even murderous ones, after particularly frustrating experiences, according to research by psychologist David Buss of the University of Texas at Austin. Such fantasies can defuse tension and thus might be considered a type of psychological hygiene. As Austrian psychoanalyst Theodor Reik put it: "A thought murder a day keeps the psychiatrist away."

But what is cleansing to a healthy mind may overwhelm a less balanced psyche. Signs of psychic trouble include being excessively introverted and lacking strong social attachments. Cho's peers described him as "quiet" and as someone who would not respond when others greeted him. Violent offenders are also often pessimistic about their future and have low self-esteem; many have been harassed, bullied or rejected by classmates; suspended from school; or pressured by teachers. Cho was reportedly teased and picked on in middle school for being shy and for his unusual way of speaking.

Adolescents who saw or otherwise experienced violence at a young age are very susceptible to intense brutal fantasies, points out clinical psychologist Al Carlisle, who practices in Price, Utah, and has long studied serial killers and young violent criminals. Such experiences, Carlisle says, foster a belief that violence is the only way to gain recognition and respect.

Thus, the media attention showered on previous school shooters such as the Columbine killers Eric Harris and Dylan Klebold often appeals greatly to would-be copycats, because the publicity may pass for esteem in their minds. After their April 1999 rampage, which left 13 dead and 24 injured at Columbine High School in Littleton, Colo., Harris and Klebold were on the covers of magazines and the front pages of newspapers for weeks.

Castillo and Bosse had stated several times that they idolized Harris and Klebold. Cho called them martyrs. On Internet fan pages Harris is compared to a god, and at a recent auction Klebold's old car fetched a price way over book value, almost as if it were a religious relic.

Evolving Apparitions

Once inspired, a disturbed adolescent may slowly tumble into an increasingly elaborate fantasy world. FBI interviews with imprisoned multiple murderers have shown that the most ominous violent fantasies gradually consume ever more psychic space. In the beginning, they may be a harmless way to pass idle hours, but later they mutate into an obsession. Eventually a dangerously violent vision dominates a youth's thoughts and cries out for action.

An unbalanced adolescent often embellishes his daydreams with details of the venue and manner of the imagined massacre--in some cases, amassing ideas from violent or violence-promoting movies, games and Web sites. Schools are a natural target because adolescents experience the worst slights in school. Two months before his rampage in Germany, Bosse wrote in his diary, "Imagine that you're standing in your old school and that your trench coat conceals all of your tools of righteousness, and then you throw the first Molotov cocktail, the first bomb. You are sending the most hated place in the world to Hell!"

As fantasies become increasingly important to a disturbed youth, he begins to neglect his real relationships to focus on the mechanics of the deed he has dreamed about. Then a serious frustration, such as the breakup of one of his last friendships, may redouble his efforts to sketch out his killing.

Would-be school shooters seem to advance ineluctably toward their idols. Copycats often wear similar clothing and choose the same weapons as those of their heroes. Among other copycat actions, Castillo wore a trench coat just as the Columbine shooters did. He also mimicked their weaponry, going so far as to name his shotgun Arlene, the same name Harris gave his shotgun. (Arlene is a character from the series of novels inspired by the 1993 computer game Doom.) Frequently, those in the final stages of planning a rampage state a desire to do it "better" than their predecessors--which generally means killing even more people.

Distorted Thoughts

Fully embellished pathological fantasies are often rationalized by a distorted sense of what is just, something that sociologist and violence researcher Jack Katz of the University of California, Los Angeles, terms "righteous slaughter." Castillo apparently felt that murdering his father was a way to right past wrongs done to his family. In a videotaped statement, the young man angrily recounts his father slapping his mother, along with him and his sister, on the head, back and rear--hitting at the camera as he speaks to it. It is not clear to what extent the abuse was real, but Castillo seemed to believe it was reason enough to kill.

Even so, Castillo wanted to be known as more than a father killer. Near the end of his final video segment, he announced: "It's time to teach history a lesson." That is where the school shooting came in. Castillo wanted to be remembered as a shooter in the tradition of Harris and Klebold. Just before the teenager was taken away from the school grounds in a police car, he yelled out to the cameras, "Columbine! Remember Columbine! Eric Harris, Dylan Klebold!"

For their part, Harris and Klebold seemed to have had more sinister motivations, with fantasies of malevolent grandeur that Katz categorizes as "primordial evil." In their diaries, published in July 2006, they painted themselves as gods who wished to be feared, not loved. One year before the killings, Klebold wrote in his school yearbook, "My wrath... will be godlike." As gods, Klebold and Harris felt they stood above society and were beyond its control--and laws. And to demonstrate their "omnipotence," they became masters of life and death.

Cho may have been trying to defend a similarly overwrought and distorted sense of morality. In his video Cho denounced materialism and hedonism, and in a note police found in his room he condemned "rich kids," perhaps suggesting that his murders were an attempt to get back at privileged people. In another video, he hinted that he would become a martyr akin to Jesus Christ, musings that echo the grander fantasies of Klebold and Harris.

Cries for Help

Although adolescents may at first hide their destructive fantasies out of fear of rejection, over time they may increasingly feel a need to express them. Bosse, for example, created drawings and poems and dropped hints of his plans in conversations. Like some other emotionally disturbed youth, Bosse cried for help. In an online forum two years before his shooting spree he wrote: "I am gorging on my entire rage, and one of these days I'm going to let it out and get revenge on all the assholes who made my life miserable.... For those of you who haven't gotten it yet: yes, I'm going to go on a rampage! I don't know what's the matter with me, I don't know what to do, please help me."

A few hours before his rampage, Bosse e-mailed a scanned copy of his diary to several schoolmates and wrote in a suicide note: "Because I know that the fascist police won't publish my videos, notebooks, or diaries or anything else, I've taken care of that myself."

In some cases, a youth may alert the media to his plans. At Virginia Tech, Cho unleashed two shooting sprees separated by two and a half hours. During that intermission, the young killer mailed a package of homemade videos, photographs and writings to NBC News. Castillo sent a video to a local newspaper in which he vented his rage and hinted that he was planning a massacre at his former school.

Such communications should not be ignored. School personnel, parents and peers alike need to be alert for verbal, written and other signs that an adolescent is becoming engulfed in a destructive fantasy world.

We are training teachers, principals and school psychologists to differentiate signs of serious trouble from ordinary adolescent rebellion. In addition to disclosing aggressive intentions, a student who is extremely interested in obtaining guns, collects movies and posters of shooters, regularly visits fan Web sites for school shooters or is a social loner is likely to be in dire need of professional help. Symptoms of depression in a young person are another warning sign. In December 2005 a physician examined Cho and found him mentally ill, noting that he had a flat affect and depressed mood.

Access to weapons is yet a further cause for alarm, indicating that the youth has the means to turn fantasy into reality. Robert Steinhauser, a 19-year-old expelled student who executed 16 people in a school in eastern Germany in 2002, was a gun club marksman who had access to enough ammunition to kill hundreds of people.

On the other hand, teachers should not panic if a student sports a rebellious hairstyle or outfit, and they should exercise judgment if someone is carrying a potentially dangerous object. In the aftermath of the Columbine killings, a student was expelled for coming to school with green hair. Another child who brought a knife to school because her mother thought it would be useful for cutting an apple was expelled after the student turned the knife in on her own. Such an overreaction perpetuates fear and hurts the students.

Seeking Respect

For kids in need of help, however, a thoughtful response to the problem is essential. School psychologists and social workers need to help disillusioned youths find a place for themselves in society, something many of them feel they lack. In one of Castillo's home videos he says: "All I wanted was respect.... No one respected me." Earning that respect might take the form of finding a job or an activity that they enjoy and in which they excel. On a broader scale, schools should offer seminars that advise students on ways to discover their talents and interests and how to use them to earn admiration.

Strong relationships with peers, teachers and other adults provide an even more effective shield against destructive fantasies. Criminologists have known for decades that building and maintaining relationships with socially accepted people is the best way to prevent violence. When a youth establishes ties to people he cares about, he is apt to feel that he has too much at stake to act out his brutal dreams.

All adolescents, not just teens at risk, should receive more social training in school. Primary violence prevention classes, for example, teach students social skills (such as empathy) and peaceful options for resolving conflicts. In addition, a teacher's role should extend beyond dispensing knowledge to forging friendships with students and providing young people with adult confidants and role models. At the same time, teachers would be advised to educate students to view critically all media that glorify violence.

The news media must take a stand as well. To make identifying with other school shooters more difficult, journalists and producers should focus less on the perpetrator, his deviant motives and the moment-by-moment unfolding of the deed--and more on the consequences of the crime.