premise: Eric Harris and Dylan Klebold, seniors at the suburban Denver school, detonated homemade bombs and opened fire with shotguns, a rifle and a semiautomatic handgun on April 20, 1999. They killed a teacher and 12 students and wounded 23 others before committing suicide. The massacre shocked the country like no other. It was the worst school assault in American history at that time, and it came in the wake of a half-dozen others. It played out on live television, watched by millions. And it represented the violent destruction of a cherished American idea: that schools in the suburbs and the countryside were havens of peace and safety.
hypothesis: 13 persons were killed by two students in 1999.