Accused teen fits no single profile

Marshfield High School junior Tobin Kerns, accused of plotting a Columbine-style massacre, shares some of the characteristics of other teenagers who have been charged with similar crimes: Kerns is 16 and male. He has distanced himself from the mainstream crowd and suffered psychological distress. And before his arrest last month on charges of plotting to kill eight people at Marshfield High, Kerns had previous run-ins with police.

But there is also much about Kerns that appears to defy the stereotype of an angry loner ready to do harm, say researchers who study adolescent killers. He has a loyal group of friends who proclaim his innocence. By all accounts, he was willing to seek therapy for his emotional swings. He also has a close relationship with his older brother, who has Down syndrome, and a girlfriend. Friends say he forms deep attachments to others.

The mixture of seemingly contradictory traits exhibited by Kerns and many teenagers who are accused of planning violence against their schools frustrates authorities' efforts to prevent such an attack.

''That's one of the many reasons there's not one profile of a school shooter," said Matt Doherty, special agent in charge at the Secret Service National Threat Assessment Center.

Since the 1999 shooting at Columbine High School near Denver, where 15 died, there have been dozens of other violent deaths in schools. Massachusetts schools have been the target of nearly a dozen threats in the past few years. Researchers keep looking for the portrait of a teenage killer, but to little avail.

Researchers for the US Secret Service, for example, looked at the cases of 41 children who committed some act of violence within their schools between 1974 and 2000. The cases involved a variety of weapons, and not every case resulted in injuries. The youngsters had only one characteristic in common: They were virtually all adolescent males. Some emerged from intact stable families; others were from fractured ones. Some were academic and athletic standouts; others were dropping out.

''If you're looking for a profile of a school shooter, it's a white male between the ages of 11 and 21 who has trouble sometimes with authority," Doherty said. ''Does that sound like someone you know?"

Reid Meloy, a California forensic psychologist, agreed that it is impossible to predict the next teenager who may arrive at school with a knife or gun. But in his many years of studying teenagers who killed multiple victims, he found they tended to share some troubling traits, he said. They are generally loners and often suffer from substance abuse as well as psychological problems. He said these teenagers also tend to have troubled family relationships.

In his study, Meloy found that adult murderers tended to act on their own and were less likely to talk about their plans. Teenagers, on the other hand, often acted in pairs and were less able to keep their plots to themselves. When they share their plans, it sometimes provides what Meloy calls the ''leakage" that tips off police. This appears to have been the case with Kerns, who, police say, became a target after tips came to them.

''It's always hard to keep a secret, and when you're a teen, it's doubly hard," Meloy said.

Researchers say the discovery that teenage killers tend to scheme over time and spill secrets can be used to the advantage of educators and police if they stay in touch with students.

If there were secret plots to tell, several of Kerns's close friends say they were never privy to them. Jeff Mattson, 22, said he cannot believe that Kerns, who spent nearly every day with his friends and girlfriend, could have crafted a murderous plot without any of them knowing. Mattson and another friend, Nikki Keating, 17, also said that Kerns never used the computer much at all, even for e-mail or playing games. However, police say that Kerns downloaded information about weapons from the Internet, an allegation that surprised his friends.

''I just can't picture something like that," Mattson said.

Kerns is being held at a juvenile detention facility in Taunton on charges that he intended to stage a Columbine-style massacre at his suburban school on the South Shore. School and law enforcement officials said this week that a grand jury has been empaneled in the case, raising the possibility that Kerns could be tried as an adult.

Police have said that Kerns exploded a homemade bomb, allegedly as a practice run, and that his home computer contained detailed plans of the school, as well as his plan to padlock certain exits. He was charged in juvenile court on Sept. 20 with eight counts of threatening to commit a crime, two counts of promoting anarchy, and one count of attempt to commit murder.

Kerns's girlfriend, Bethany Lunn, 17, said she remains concerned about his well-being. She said she heard that guards at the detention center where he is being watched were on alert for signs of suicide, which her boyfriend had exhibited at least once before.

''I feel so bad he's in this position," said Lunn.

Kerns's father, Ben, 48, said he had his youngest of two sons admitted into a Brockton mental health facility after discovering a suicide note last year. The father said that for years Kerns has suffered post-traumatic stress disorder, which the elder Kerns said was the result of psychological and emotional abuse his son had suffered in his childhood.

Ben Kerns did not elaborate on the specifics of the abuse, other than to say it had to do with his son's troubled relationship with his mother, Jean Tracy. The boy's parents divorced in 1997.

Tracy -- who currently resides in Scottsdale, Ariz. -- has not returned repeated phone calls to her home.

Since she turned over physical custody of the boys in 1999, she had made some visits to Massachusetts, including the high school graduation of her older son, Andy, as well as at Kerns's arraignment last month.

Lunn said Kerns was struggling to reconcile with his mother. ''He was coping with his feelings about his mother," Lunn said.

Friends acknowledge that Kerns Tobin was a troubled teen who had past brushes with the law, including vandalism and stealing. He sometimes smoked cigarettes outside school instead of attending classes. But that degree of secrecy, they said, does not make him a student capable of plotting murder -- let alone executing it.

Researchers who study adolescent killers say anything is possible in the world of teenage violence, including someone keeping a murderous plot entirely to himself. But that is not typical, they said, for this age group.

''Part of it is being an adolescent," said Meloy, the forensic psychologist. ''They need to interact closely with friends."

Patricia Wen can be reached at wen@globe.com