On April 20, 1999, two high school students walked into their Colorado high school, planted bombs and opened fire on their classmates, killing 12 teenagers and one teacher and wounding over 20 others. They then turned the guns on themselves.
At the time, the massacre at Columbine High School in Littleton, Colorado, was the deadliest school shooting in American history.
Dressed in trench coats, the gunmen, Eric Harris, 18, and Dylan Klebold, 17, walked into their high school just after 11 a.m., placing two duffel bags in the cafeteria, each containing 20-pound bombs made of propane tanks set to explode at 11:17 a.m. They walked out of the school, went to their respective cars in the parking lot and waited for the bombs to explode.
When the bombs never went off, at 11:19 a.m. the duo began firing outside the school before going inside and reverting to a so-called Plan B. Once inside, they started throwing homemade explosives they dubbed "crickets" to inflict further destruction.
They spent less than an hour inside, shooting teachers and classmates, before eventually taking their own lives at 12:08.
Earlier that morning, they had also placed a bomb deep in the woods nearby. They hoped it would explode, creating a diversion for authorities so that by the time the school massacre began, they would be too stretched to contain both areas. However, the plan went awry when the bomb in the woods only sparked a small fire.
SWAT teams entered the school 47 minutes after the shootings started; it would take five hours before law enforcement would officially declare the school under control.
The attack rattled America to its core as rock music, goth fashion and violent video games came under scrutiny for allegedly inspiring the shooters.
Originally it was thought that the violence was because of bullying the two men faced by their classmates, but investigators later determined that wasn't the case. It was just one of the many myths surrounding the shooting that would later be debunked.
"The narrative that was shared after Columbine, people still believe that today," former Columbine High School principal Frank "Mr. De" DeAngelis told Inside Edition ahead of the 20th anniversary of the tragedy.
DeAngelis worked at the school for 35 years and served as principal for 18 years, including the day of the shooting. He details his experience in a new book, "They Call Me 'Mr. De.'" DeAngelis retired in 2014.
"I am not going to say that Columbine was this perfect high school," he said. "We had bullying going on. We were a typical high school but what scares me is the way the media portrayed these two as being bullied ... and that is what led them to do what they did."
Harris and Klebold were A-grade students who worked together at a local pizzeria. Harris was known for his charm and calm disposition while Klebold was known as his sidekick.
It was claimed at the time that the gunmen were interested in goth culture, but no evidence has emerged to support those assertions. It was also reported that the shooters were fans of shock rocker Marilyn Manson, who took much of the media heat in the wake of the shooting.
“It was unthinkable that these kids did not have a simple black-and-white reason for their actions," Marilyn Manson wrote in Rolling Stone months after the shooting. "And so a scapegoat was needed. I remember hearing the initial reports from Littleton, that Harris and Klebold were wearing makeup and were dressed like Marilyn Manson, whom they obviously must worship, since they were dressed in black.
"Of course, speculation snowballed into making me the poster boy for everything that is bad in the world. These two idiots weren’t wearing makeup, and they weren’t dressed like me or like goths."
Goths whom Inside Edition spoke to in the aftermath of the shootings stressed that the culture is not violent and that wearing a trench coat did not make you a killer. Harris and Klebold were initially thought to have been part of goth groups in the area, however, that was not the case according to members.
It was reported in the immediate aftermath that the killers belonged to a group called the Trench Coat Mafia due to the outfits they were wearing the day of the shooting. However, members of the group told Inside Edition that while they knew the killers, they were not affiliated with them nor was the Trench Coat Mafia a violent sect.
“I can’t even watch violence on television, I close my eyes,” said Krista, a member of the Trench Coat Mafia who asked that Inside Edition only use her first name in a 1999 interview. “I never realized how much hatred people could hold in them until now.”
She said that the public perception of the Trench Coat Mafia was all wrong and they “were a normal group of friends” who would do average teenage things like going to the mall, to the movies and out to eat.
The German industrial band KMFDM were also scrutinized after it was discovered that their lyrics were posted on a website by Harris. The band had no link to the shooters and called their music "an art form not a political party."
It was also reported that the gunmen were ostracized from their classmates, however, that was not the case, according to DeAngelis.
"These were not these outcasts as they were portrayed in the media. What I saw was the ones who were in advanced placement classes, I saw [Klebold] who was going to the University of Arizona because he had been accepted. … Klebold was at prom that Saturday night high-fiving me and here is Eric, who was at the after-prom. What we saw were kids actively involved in school activities," he said.
The shooters picked their victims randomly, according to authorities, which contradicted initial reports that suggested they targeted athletes, Christians and minorities.
Investigators also said that diaries recovered from the shooters’ bedrooms had passages and plans that were inspired by Oklahoma City bomber Timothy McVeigh. They planned their attack around the four-year anniversary of the April 19, 1995, tragedy. However, due to complications in attaining ammunition, the carnage was pushed back a day, according to reports.
The bombs were made in the homes of the shooters' parents by the killers themselves. They reportedly obtained their weapon arsenal through friends who were older than they were but had no idea what the guns would be used for, according to authorities and author Dave Cullen, whose best-seller, "Columbine," chronicled the lead up and aftermath of the shootings.
“Harris quietly despised the people he took so much trouble to charm and could not wait to see them all die horrible deaths,” Guardian writer Andrew Gumbel, who covered the shooting, wrote in 2009.
Klebold, meanwhile, was convinced he was a failure, according to Gumbel. The two fed off each other's self-loathing and disdain for the people around them.
"They created these 'Basement Tapes' they made a year prior and in those tapes there was very little mention about being bullied and being picked on," DeAngelis said. "But what I did hear was a person who idolized Adolf Hitler, who talked about 'survival of the fittest' and [that] people deserved to die because they are weak individuals."
He added, "The last comment they made prior to coming to Columbine High School and taping their farewell song ... is they said, 'It is unfortunate that someone didn’t find these tapes before it was too late.'"
DeAngelis said he made a promise to his faculty, staff, community, and students that he would be there for each of them after the attack.
"There were teachers that saw things that no human being should have to see," he said.
Days after the shooting, funerals began to take place in and around Littleton for the victims — and the perpetrators. Klebold’s funeral was attended by 15 people and soon after his family’s reverend, Don Marxhausen, who performed the service, spoke to Inside Edition.
"They just know their son who they loved was getting ready for college," he said. "There is the grief of the death of a child — which is the ultimate, I guess, loss. Then there is this now, who was this child and why did this happen?"
Michael Shoals, the father of one of the victims, Isaiah, spoke to Inside Edition in the days after his son was murdered, criticizing the killers' parents for not paying attention to what their kids were doing.
“I can’t really say much for the other parents ... they didn’t watch [their kids] because there is no way bombs would be made in this garage and I didn’t know about it,” he said.
In the aftermath of the shootings, the school has been closed each April 20. A memorial was erected on the campus grounds for friends, family and future students to pay their respects to those who lost their lives that day.