Dylan Klebold was born in Lakewood, Colorado, to Thomas and Susan Klebold. His parents were pacifists and attended a Lutheran church with their children, and Dylan and his older brother, Byron, attended confirmation classes in accordance with Lutheran tradition. At home, the family also observed some rituals in keeping with Klebold’s maternal grandfather’s Jewish heritage. Klebold attended Normandy Elementary in Littleton, Colorado for the first two grades before transferring to Governor’s Ranch Elementary and became part of the CHIPS (“Challenging High Intellectual Potential Students”) program. He found the transition to Ken Caryl Middle School difficult.

At Columbine High, Eric Harris and Dylan Klebold were active in school play productions, operated video productions and became computer assistants maintaining the school’s computer server. According to early accounts of the shooting, Harris and Klebold were very unpopular students and targets of bullying. While sources do support accounts of bullying directed toward the pair, accounts of them being outcasts have been reported to be false. Eric Harris and Klebold were initially reported to be members of a group that called themselves the “Trenchcoat Mafia”, although in truth they had no particular connection with the group, and did not appear in a group photo of the Trenchcoat Mafia in the 1998 Columbine yearbook. Harris’s father stated that his son was “a member of what they call the Trenchcoat Mafia” in a 911 call he made on April 20, 1999. Klebold attended the high school prom three days before the shootings with a classmate named Robyn Anderson.

Eric Harris and Klebold linked their personal computers on a network and both played many games over the Internet. Harris created a set of levels for the game Doom, which later became known as the ‘Harris levels’. Harris had a web presence under the handle “REB” (short for Rebel, a nod to the nickname of Columbine’s sports teams) and other cyber aliases, including “Rebldomakr”, “Rebdoomer”, and “Rebdomine”, while Klebold went by the names “VoDKa” and “VoDkA”. Harris had various websites that hosted Doom and Quake files, as well as team information for those he gamed with online. The sites openly espoused hatred for the people of their neighborhood and the world in general. When the pair began experimenting with pipe bombs, they posted results of the explosions on the websites. The website was shut down by America Online after the shootings and was preserved for the FBI. In December 1998, Eric Harris and Klebold made Hitmen for Hire, a video for a school project in which they swore, yelled at the camera, made violent statements, and acted out shooting and killing students in the hallway of their school as Hitmen for Hire. They both displayed themes of violence in their creative writing projects for school; of a Doom-based story written by Harris on January 17, 1999, Harris’s teacher said: “Yours is a unique approach and your writing works in a gruesome way — good details and mood setting.”

On April 20, 1999, while smoking a cigarette at the start of lunch break, Brooks Brown saw Eric Harris arrive at school. Brown had severed his friendship with Harris a year earlier because Harris had thrown a chunk of ice at his car windshield; Brown patched things up with Harris just prior to the shooting. Brown scolded Harris for skipping the morning class, because Harris was always serious about schoolwork and being on time. Harris reportedly said, “It doesn’t matter anymore” and also said, “Brooks, I like you now. Get out of here. Go home.” Brown quickly left the school grounds. At 11:19 a.m., he heard the first gunshots after he had walked some distance away from the school, and he informed the police via a neighbor’s cell phone. By that time, Dylan Klebold had already arrived at the school in a separate car, and the two boys left two gym bags, each containing a 20-pound propane bomb, inside the school cafeteria. When these devices failed to detonate, Harris and Klebold launched a shooting attack against their classmates. It remains the deadliest attack ever perpetrated at an American high school. Harris was responsible for eight of the thirteen confirmed deaths (Rachel Scott, Daniel Rohrbough, a teacher identified as Dave Sanders, Steve Curnow, Cassie Bernall, Isaiah Shoels, Kelly Fleming, and Daniel Mauser), while Klebold was responsible for the remaining five (Kyle Velasquez, Matthew Kechter, Lauren Townsend, John Tomlin and Corey DePooter). There were 24 wounded, most in critical condition.

At 12:02 p.m., Harris and Dylan Klebold returned to the library. This was 20 minutes after their lethal shooting spree had ended, leaving 12 students dead, one teacher dying, and another 24 students and staff injured. Ten of their victims had been killed in the library, with their bodies strewn about the floor. Harris and Klebold went to the west windows and opened fire on the police outside. Six minutes later, they walked to the bookshelves near a table where Patrick Ireland lay badly-wounded and unconscious. Student Lisa Kreutz, injured in the earlier library attack, was also in the room, unable to move. At 12:08 p.m., art teacher Patti Nielson, who had locked herself inside a break room with student Brian Anderson and library staff, overheard Harris and Klebold shout out in unison: “One! Two! Three!” followed immediately by the sound of gunfire. Eric Harris had fired his shotgun through the roof of his mouth, and Dylan Klebold had shot himself in the left temple with his TEC-9 semi-automatic handgun.