See Evil, Hear Evil, Speak Evil.

Silence can be deadly. By speaking up, teen informers may have averted four separate Columbine-style school attacks.

At high schools in Colorado, New York, and Kansas, and at a college in California, students recently tipped off authorities after learning about fellow teens stockpiling weapons and planning massacres. "When I thought these guys could kill my friends, and even themselves, I knew I couldn't live with myself if anything happened," says a girl in Fort Collins, Colorado, who had heard talk of a re-enactment of the Columbine shooting being planned for its second anniversary in April.

Experts say that in almost three-fourths of the 37 school shootings since 1974, the assailant told someone in advance about the plan, almost always a fellow student. James Alan Fox, a professor of criminology at Northeastern University, says the attitude on snitching is shifting for the better. "The code used to be, snitching was the lowest form of human behavior for kids," he says. "Now there have been so many forums and events about Columbine at schools that we are encouraging and rewarding snitching."