Twenty-one additional people were injured by gunshots, and gunfire was exchanged with the police. Another three people were injured trying to escape. The Columbine massacre was the deadliest mass shooting at a K school in U. As of [update] , Columbine is still the deadliest school shooting in Colorado , the deadliest high school shooting in the United States to happen west of the Mississippi River , and one of the deadliest mass shootings in the United States.
Harris and Klebold, who planned for roughly a year, and hoped to have a large number of victims, intended for the attack to primarily be a bombing and only secondarily a shooting. However, the pair chose to launch a shooting attack after the several homemade bombs they planted in the school failed to detonate.
Their motive remains inconclusive. The police were slow to enter the school and were heavily criticized for not intervening during the shooting. The incident resulted in the introduction of the immediate action rapid deployment IARD tactic, which is used in active-shooter situations, and an increased emphasis on school security with zero-tolerance policies. The violence sparked debates over American gun culture and gun control laws , high school cliques , subcultures e.
Many makeshift memorials were created after the massacre, including ones employing victims Rachel Scott 's car and John Tomlin's truck. Fifteen crosses for the victims and the shooters were erected on top of a hill in Clement Park.
The crosses for Harris and Klebold were later removed following controversy. Planning for a permanent memorial began in June , and the resulting Columbine Memorial opened to the public in September The shooting has inspired dozens of copycat killings, dubbed the Columbine effect , including many deadlier shootings across the world.
