Before the shooting, Harris and Klebold, matured 18 and 17, made home recordings alluding to what they would do and apologizing to their parents for it. On April 20, 1999, at around 11.29 AM, they carried bombs and firearms and opened fire inside Columbine High School.

They murdered 13 people, twelve of them understudies and one teacher, and injured 23 others. At that point, they killed themselves in the school's library at roughly 12.08 PM by shooting themselves in the head.

Eric Harris
Harris was born in Wichita, Kansas. The Harris family relocated often, as Eric's father, Wayne Harris, was a U.S. Air Force transport pilot. His mother, Katherine Ann Poole, was a homemaker. The family moved from Plattsburgh, New York, to Littleton, Colorado, in July 1993, when Wayne Harris retired from military service.

The Harris family lived in rented accommodations for the first three years that they lived in the Littleton area. During this time, Eric met Dylan Klebold. In 1996, the Harris family purchased a house south of Columbine High School. Eric's older brother, Kevin, attended college at the University of Colorado Boulder.

Dylan Klebold
Klebold was born in Lakewood, Colorado, to Thomas and Susan Klebold. His parents were pacifists and attended a Lutheran church with their children. Both Dylan and his older brother, Byron, attended confirmation classes in accordance with the Lutheran tradition. As had been the case with his older brother, Dylan was named after a renowned poet – in Dylan's case, the playwright Dylan Thomas.

At the family home, the Klebolds 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.