At approximately 11:19 a.m., Dylan Klebold and Eric Harris, dressed in trench coats, began shooting fellow students outside Columbine High School, located in a suburb south of Denver. The pair then moved inside the school, where they gunned down many of their victims in the library.

By approximately 11:35 a.m., Klebold and Harris had killed 12 students and a teacher and wounded more than 20 other people. Shortly after 12 p.m., the two teens turned their guns on themselves.

Investigators later learned Harris and Klebold had arrived in separate cars at Columbine around 11:10 on the morning of the massacre. The two then walked into the school cafeteria, where they placed two duffel bags each containing a 20-pound propane bomb set to explode at 11:17 a.m.

The teens then went back outside to their cars to wait for the bombs to go off. When the bombs failed to detonate, Harris and Klebold began their shooting spree.

Victims of the Columbine shooting include Cassie Bernall, 17; Steven Curnow, 14; Corey DePooter, 17; Kelly Fleming, 16; Matthew Kechter, 16; Daniel Mauser, 15; Daniel Rohrbough, 15; William "Dave" Sanders, 47; Rachel Scott, 17; Isaiah Shoels, 18; John Tomlin, 16; Lauren Townsend, 18, and Kyle Velasquez, 16.

In the days immediately following the shootings, it was speculated that Harris and Klebold purposely chose athletes, minorities and Christians as their victims.

It initially was reported that one student, Cassie Bernall, was asked by one of the gunmen if she believed in God. When Bernall allegedly said, “Yes,” she was shot to death. Her parents later wrote a book titled She Said Yes, honoring their daughter.

However, it later was determined the question was not posed to Bernall but to another student who already had been wounded by a gunshot. When that victim replied, “Yes,” the shooter walked away.

Subsequent investigations determined Harris and Klebold chose their victims randomly, and the two teens originally had intended to bomb their school, potentially killing hundreds of people.

There was speculation that Harris and Klebold committed the killings because they were members of a group of social outcasts called the Trenchcoat Mafia that was fascinated by Goth culture. It also was speculated that Harris and Klebold had carried out the shootings as retaliation for being bullied.

Additionally, violent video games and music were blamed for influencing the killers. However, none of these theories was ever proven.

Through journals left behind by Harris and Klebold, investigators eventually discovered the teens had been planning for a year to bomb the school in an attack similar to the 1995 Oklahoma City bombing.

Investigative journalist Dave Cullen, author of the 2009 book Columbine, described Harris as “the callously brutal mastermind,” while Klebold was a “quivering depressive who journaled obsessively about love and attended the Columbine prom three days before opening fire.”

In the aftermath of the shootings, many schools across America enacted “zero-tolerance” rules regarding disruptive behavior and threats of violence from students. Columbine High School reopened in the fall of 1999, but the massacre left a scar on the Littleton community.

Mark Manes, the man who sold a gun to Harris and bought him 100 rounds of ammunition the day before the murders, was sentenced to six years in prison. Another man, Philip Duran, who introduced Harris and Klebold to Manes, also was sentenced to prison time.

Some victims and families of people killed or injured filed suit against the school and the police; most of these suits were later dismissed in court.

The list of school shootings in the United States grows longer every year, and includes the Virginia Tech shooting in 2007, the Sandy Hook Elementary School shooting in 2012, the Robb Elementary shooting in 2022, the University of Texas tower shooting in 1966, the Marjory Stoneman Douglas High School shooting in 2018, the Santa Fe High School shooting in 2018 and the Umpqua Community College shooting in 2015, among others.

Gun control and disagreements over the interpretation of the Second Amendment continue to be a controversial issue in the United States, where 45,000 people die from gun-related injuries each year.