TWO of America's most famous law-enforcement agencies are turning their attention from terrorists to children.
The FBI and Secret Service have separately offered to help educators recognise violent pupils so they can intervene to prevent incidents such as the Columbine high-school killings.
The FBI has prepared a report listing the likely characteristics of children who may be dangerous.
And the Secret Service - which protects the President, and other VIPs - is sharing the methods it uses to help thwart assassins.
Investigators and psychologists from both agencies interviewed the perpetrators of, and witnesses to, 40 school shootings, including Columbine, over more than two years. But they differ significantly in the ways they suggest potential killers might be identified.
The FBI lists 28 traits it says indicate whether a pupil who has threatened a violent act will actually carry it out. "We must continue to search for those crucial indicators which suggest that a threat of school violence may be real," said Attorney General Janet Reno, who oversees the FBI.
The FBI report says school killers share certain traits (see box). However, the Secret Service, whih will release its report later in the autumn - has dismissed such "profiling", and urged schools to focus on behaviour and motives alone, just as it does when weighing threats made against political leaders.
It disputes the idea that student criminals have common characteristics, saying that some recent killers have been victims of bullies while others have not, and that some were very bright while others were under-achievers.
Secret Service officials observed that many school shootings were preceded by threatening comments, if not overt warnings directed at the target.
None of the killers had acted impulsively, instead planning their crimes in advance. Many wrote in diaries and on websites, and spoke about them to classmates. And, while some had psychological problems, they were not necessarily visibly psychotic.
Child psychologists responded to the move by warning that a list of dangerous traits might prompt schools to suspect innocent students. Many adolescents make idle threats or practise non-conformist behaviour, they said.
The FBI says school killers share the following attributes:
access to weapons,
drug and alcohol problems,
tendency toward inappropriate humour, and
unlimited TV and Internet use.