the columbine high school massacre was a school shooting and attempted bombing at columbine high school in littleton, colorado, near denver, that happened on april 20, 1999. eighteen-year-old eric harris and 17-year-old dylan klebold carried out the massacre and were both students at the school. they murdered 12 students and one teacher using guns. ten of the murders happened in the school's library, where they then killed themselves with their guns. before the shootings, they had planted two large propane bombs in the school's cafeteria. they could have killed many people in there, but they did not explode. they also planted two car bombs in the school's parking lot, which were supposed to kill first responders and news reporters. they also did not explode. they also carried pipe bombs and molotov cocktails, which they lit and threw. most of them exploded but nobody was injured or killed by any of the bombs used during the massacre.