The study, conducted in co-operation with educators and mental health experts, also blames violent entertainment, relentless media coverage of killings, lax parental involvement, a lack of trained school staff and the availability of guns. The report comes as Kip Kinkel, a 17-year-old who killed his parents and then gunned down two students during a rampage in his school cafeteria in Oregon, was sentenced to 112 years in prison.
The experts now will try to reach consensus on how to prevent such shootings. Among other steps, they have prepared a list of 50 "risk factors" to help pick out children who could become killers. They include aggressive outbursts, a history of violence or abuse in the family, threats to commit violent acts, 40 hours or more per week viewing violent entertainment, and having a gun in the house.
Youth counsellors say the signs are usually clear. Mr Kinkel, for instance, kept a journal filled with rage, self-loathing and fantasies of violence. One of the Columbine shooters, Eric Harris, posted threats on his website.