A massacre in 1999, which happened at Columbine High School in Amrica, when two senior students (Eric Harris and Dylan Klebold) attempted to blow up their school with two propane bombs and then kill the survivors with firearms (a Tec9
, a Sawn off Shotgun and some other stuff).
Luckily, both bombs failed to detonate. They started shooting students as they went into the school, people heard the gun shots and rang the fire alarm saving the majority of the school.They went into the commons (where they had placed the propane bombs) and tried to set them off, when this failed they proceded into the libary where they killed the majority of the students.
After that, It is presumed they both shot themselfs in the head.