Mass murders in Colorado

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.

mass shooting in a movie theater in the United States

massacre of a village of Cheyenne and Arapaho people in the American Indian Wars

attack by Colorado National Guard and mine camp guards on striking coal miners

murders by Chris Watts of his wife and daughters in Colorado in 2018

flight

shooting at grocery store on March 22, 2021 in Boulder, Colorado

shooting at an LGBTQ bar on November 19–20, 2022 in Colorado Springs, Colorado

mass shooting at a medical clinic in Colorado on November 27, 2015

1927 police shooting of striking miners in Serene, Colorado, United States