Improvised explosive device bombings in 1999

On April 20, 1999, twelfth-grade students Eric Harris and Dylan Klebold murdered 13 students and 1 teacher in a school shooting and attempted bombing at Columbine High School in Columbine, Colorado, United States. Twenty people were injured by the gunfire, and three others were injured while trying to escape. The attack ended when Harris and Klebold died by suicide. The Columbine massacre was the deadliest mass shooting at a K–12 school in U.S. history until the Sandy Hook Elementary School shooting in December 2012. It remains among the most infamous massacres in the United States and the deadliest mass shooting in Colorado. As of June 2025, it had inspired more than 70 copycat attacks, a phenomenon dubbed the Columbine effect, and Columbine has become a byword for modern school shootings.