Columbine school shooting 1999

Police stand outside the east entrance of Columbine High school as bomb squads and SWAT teams secure students April 20, 1999, in Littleton, Colo. Thirteen students and one teacher died, making it one of the deadliest school shootings in U.S. history. Dylan Klebold, 17, and Eric Harris, 18, stormed the school with bombs, shotguns and semi-automatic weapons and began their killing spree. The two committed suicide during their rampage.

Credit: MARK LEFFINGWELL/AFP/Getty Images