On April 20, 1999, Eric Harris and Dylan Klebold carried out a school shooting and attempted bombing at Columbine High School in Columbine, Colorado, killing 12 students and one teacher inside the school and another student outside before dying by suicide. Planned for about a year and intended primarily as a bombing, the attack escalated when homemade bombs failed to explode. It left 20 people wounded by gunfire and three others injured while escaping. The massacre became one of the most infamous acts of violence in modern American history, reshaping police tactics, fueling national debates, and remaining a powerful symbol of school violence and its aftermath.