In the following years, various media outlets attributed multiple motivating factors to the attack, including bullying, mental illness, racism, psychiatric medication, and violence in music, movies, and video games.

Harris and Klebold have become pop culture icons, with the pair often portrayed, referenced and seen in film, television, video games, music and books.

Klebold was soon diagnosed with pyloric stenosis, a condition in which the opening between the stomach and small intestines thickens, causing severe vomiting during the first few months of life.

[33] Much of the information on Harris and Klebold's friendship is unknown, on their interactions and conversations, aside from the Basement Tapes, of which only transcripts have been released, aside from a short audio clip recorded surreptitiously by a victim's father.

Over time, they became increasingly close, hanging out by often going out bowling, carpooling and playing the video game Doom over a private server connected to their personal computers.

Harris had a web presence under the handle "REB" (short for Rebel, a nod to the nickname of Columbine High's sports teams) and other online aliases, including "Rebldomakr", "Rebdoomer", and "Rebdomine".

They both left good impressions on juvenile officers, who offered to expunge their criminal records if they agreed to attend a diversionary program which included community service and psychiatric treatment.

Regarding Harris, it was remarked that he was "a very bright individual who is likely to succeed in life", while Klebold was said to be intelligent, but "needs to understand that hard work is part of fulfilling a dream.

[62] In the letter, Harris expressed regret about his actions; however, in one of his journal entries dated April 12, he wrote: "Isn't america supposed to be the land of the free?

[63][64] When an economics class had Harris make an ad for a business, he and Klebold made a video called Hitmen for Hire on December 8, 1998, which was released in February 2004.

[66][d] They wore black trench coats on the day of the massacre, and the video seemed a kind of dress rehearsal, showing them walking the halls of the school, and shooting bullies outside with fake guns.

In violation of federal law, Russell failed to keep records of the sale, yet he determined that the purchaser of the gun was twenty-one years of age or older.

Several residents of the area claimed to have heard glass breaking and buzzing sounds from the Harris family's garage, which later was concluded to indicate they were constructing pipe bombs.

[14] It was estimated that if any of the bombs placed in the cafeteria had detonated properly, the blast could have caused extensive structural damage to the school and would have resulted in hundreds of casualties.

[81] By that time, Klebold had already arrived at the school in a separate car, and the two boys left two duffel bags, each containing a 20-pound propane bomb, inside the cafeteria.

[83][84] Harris was responsible for eight of the thirteen confirmed deaths (Rachel Scott, Daniel Rohrbough,[85] teacher 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).

Just before shooting himself, Klebold lit a Molotov cocktail on a nearby table, underneath which Ireland was lying, which caused the tabletop to momentarily catch fire.

In his journal, Harris mentioned his admiration of what he imagined to be natural selection, and wrote that he would like to put everyone in a super Doom game and see to it that the weak die and the strong live.

[116] Harris began keeping a journal in April 1998, a short time after the pair was charged with breaking into a van, for which each received ten months of juvenile intervention counseling and community service in January 1998.

Though some friends of Harris suggested that he had stopped taking the drug beforehand,[117] the autopsy reports showed low therapeutic or normal (not toxic or lethal) blood-levels of fluvoxamine in his system, which was around 0.0031–0.0087 mg/ml,[118] at the time of death.

[119] After the shootings, opponents of contemporary psychiatry like Peter Breggin[120] claimed that the psychiatric medications prescribed to Harris after his conviction may have exacerbated his aggressiveness.

[122] For the rest of his writings, Klebold often wrote about his view that he and Harris were "god-like" and more highly evolved than every other human being, but his secret journal records the aforementioned self-loathing and suicidal intentions.

", to which he replied, "I wouldn't say a single word to them—I would listen to what they have to say, and that's what no one did", referring to people ignoring red flags that rose from Harris and Klebold prior to the shooting.

[9] According to psychologist Peter Langman, Klebold displayed signs of schizotypal personality disorder – he struck many people as odd due to his shy nature, appeared to have had disturbed thought processes and constantly misused language in unusual ways as evidenced by his journal.

"[133] In Andrew Solomon's 2012 book Far from the Tree, she acknowledged that on the day of the massacre, when she discovered that Klebold was one of the shooters, she prayed he would kill himself (before committing mass murder).

"[140] ITV describes the legacy of Harris and Klebold as deadly, as they have inspired several instances of mass killings in the United States and globally.

[147] Ralph Larkin examined twelve major school shootings in the US in the following eight years and found that in eight of those, "the shooters made explicit reference to Harris and Klebold.

[152] In 2015, journalist Malcolm Gladwell writing in The New Yorker magazine proposed a threshold model of school shootings in which Harris and Klebold were the triggering actors in "a slow-motion, ever-evolving riot, in which each new participant's action makes sense in reaction to and in combination with those who came before.

[157] The 2002 Michael Moore documentary film Bowling for Columbine focuses heavily on a perceived American obsession with handguns, its grip on Jefferson County, Colorado, and its role in the shooting.

"[160] The 2016 biographical film I'm Not Ashamed, based on the journals of Rachel Scott, includes glimpses of Harris's and Klebold's lives and of interactions between them and other students at Columbine High School.