On this day nineteen years ago, Eric Harris and Dylan Klebold killed twelve of their classmates and a teacher, and wounded twenty-three others, at Columbine High School in Littleton, Colorado. As the nation watched the chaos unfold on television for more than five hours, a narrative emerged and took hold that members of a so-called Trenchcoat Mafia brought their guns to school so as to exact their revenge on jocks and other bullies. From this event came the image of “the school shooter.” But the shooters left evidence that tells a very different story. Harris’s diary suggests that he was launching an act of domestic terrorism, whose roots extended back through the bombing of the Oklahoma City Federal Building in 1995 and the 1993 standoff between federal authorities and a cult known as the Branch Davidians in Waco, Texas.

Eric Harris and Dylan Klebold were running late to school on the morning of April 20, 1999. They had neither a test nor any important academic commitment, but 11:17 am was when there would be “maximum human density” in the lunchroom—the largest concentration of students—with about 600 or so in one central location. They placed a decoy bomb in a field a few miles away and left their cars in the parking lot loaded with propane, gasoline, and timers set to trigger the vehicles to explode. They walked into the building with their duffel bags of propane tanks with timed explosives, pipe bombs, and small arsenal of firearms. When the timers did not ignite the bombs at 11:17, the boys panicked. They pulled out shotguns and began shooting.

In the hours after the shooting, reporters rushed to the scene to interview anyone connected with the school. As hundreds of students poured into streets, parking lots, homes, and nearby Clement Park to escape the gunmen, they were met by account-hungry reporters. The Denver Post dispatched fifty staff members to the scene to capture the moment, and other media outlets used their information, footage, and accounts. News anchors did not verify their information and reported rumors, which began to consolidate around the idea that Columbine was a “toxic” place to go to school. Bullying ran amok, unchecked by teachers and administrators, and the result was angry outcasts.

But in fact, Dylan Klebold was a depressed young man who thought extensively about suicide, and Eric Harris was well-liked, kept a cool head under pressure, and manipulated those around him without any apparent consideration for the feelings of others. Columbine was not a story of bullied teenagers. It was instead linked to teenage depression and, especially in the case of Eric Harris, to a desire to become a domestic terrorist.

According to Dave Cullen, the journalist who spent more than a decade studying the massacre at Columbine, Eric Harris was fixated on, among other things, the bombing of the Alfred P. Murrah Federal Building in Oklahoma City. On April 19, 1995, a Gulf War veteran named Timothy McVeigh blew up that building, killing 168 people, including nineteen children under the age of six, and injuring more than 800 others. When apprehended, McVeigh was wearing a t-shirt with Abraham Lincoln’s picture and the phrase “sic semper tyrannis”—thus always to tyrants—the line shouted by John Wilkes Booth as he leapt to the stage after shooting Lincoln in his booth at Ford’s Theater.

McVeigh took inspiration from Booth but he was also motivated by the raid conducted by federal agents on the Branch Davidian compound in Waco, Texas, exactly two years before he blew up the Murrah Federal Building. There, following a fifty-one day siege, authorities using tanks and tear gas looked to apprehend cult leader David Koresh and liberate his eighty-four hostages, only to have a fire break out that resulted in the deaths of more than seventy-five people. To McVeigh, who witnessed the carnage from a hill three miles away, Waco was a sign that the government of the United States had devolved into socialism and that it would stop at nothing to usurp the individual freedoms of American citizens. As he later said: “What the U.S. government did at Waco and Ruby Ridge was dirty. I gave dirty back to them at Oklahoma City.”

While there is no direct evidence that Eric Harris watched coverage of McVeigh’s trial, which took place in Denver, sixteen miles from Littleton, his diary entries indicate that McVeigh had a profound impact on his thinking and that he believed McVeigh had not gone far enough. As Dave Cullen writes: “In his journal, Eric would brag about topping McVeigh. Oklahoma City was a one-note performance. McVeigh set his timer and walked away. He didn’t even see his spectacle unfold.”

Harris strived for a bigger and better attack than Oklahoma City, and he wanted to be at the center of it. “God I want to torch and level everything,” he wrote in his journal. His attack would be “like the LA riots, the oklahoma bombing, WWII, vietnam, duke and doom all mixed together” and “Judgement Day” would come on Monday, April 19, 1999, the anniversary of the Waco and Oklahoma City bombings. But on Sunday night, April 18, Harris only had seven hundred rounds of ammunition, and he wanted more. A friend came through, but not until the following night, which meant the attack on Columbine High School would have to come on the day after the anniversary instead: Tuesday, April 20.

Although Harris and Klebold killed their victims with guns, it is clear that they planned a bombing rather than a shooting. The guns they packed were secondary weapons to be used against fleeing survivors. In the event, some of the bombs exploded while others failed. Had all the bombs worked, hundreds would have died, dwarfing the death toll of Oklahoma City. Only the misunderstanding of Harris and Klebold with regard to things like explosive reactions and electrical circuitry spared those lives.

Harris indicated that if he and Klebold managed to escape without being killed by the authorities, they would “hijack a hell of a lot of bombs and crash a plane into NYC… just something to cause more devastation.” Perhaps this was a reference to the 1993 World Trade Center bombing—perhaps not. But Harris’s plans make it clear that what happened on April 20, 1999, was not an attempt to take revenge on some bullies.