Nearly thirty minutes into one of the most infamous school shootings in history, with dozens of victims still cowering and crying beneath tables in the library, Eric Harris and Dylan Klebold unanimously and almost intuitively stopped firing their guns. It was as if their inner timer had reached zero, as if they were being beckoned to the school’s cafeteria. There, the two teenagers tried to set-off a slew of propane-tank bombs they’d dropped off in duffel bags earlier. None exploded (Harris and Klebold’s journal entries fantasized an elaborate bombing; when many of their homemade explosives failed to detonate, the two resorted to shooting). Then, seemingly bored and unbothered, the duo returned to the library to claim their final victims. With the Rocky Mountains in sight through a nearby window, Harris and Klebold committed suicide – the former through his mouth and the latter at his temple. These are the events leading up to that moment:

April 20, 1999, 5:30 a.m.:

The boys leave their respective homes to organize and prepare.

11:10 a.m.:

Eric Harris parks his 1986 gray Honda Civic in a spot assigned to another student. Dylan Klebold, in his 1982 black BMW, does the same. Both cars, brimming with bombs, strategically “flank the school’s cafeteria and the exits and entrances into the lower level.”

On his way into the school, Harris tells an acquaintance, Brooks Brown, to flee the premises because “he likes him.” Brown listens.

Brown would later refute the theory that Harris and Klebold had been bullied.

11: 14 a.m.:

Harris and Klebold make their way into the cafeteria with duffel bags full of explosives timed to go off at 11:17 a.m.. They leave the duffel bags behind, perfectly camouflaged by the 400 backpacks already strewn about the cafeteria floor.

11:17 a.m.:

Harris and Klebold return to their cars and await the mayhem. According to their plans, the two intended to shoot any escaping survivors.

11:19 a.m.:

Diversionary bombs left in a field three miles southwest of Columbine High School serve their purpose. A call is made to the Jefferson County Dispatch Center about an explosion and small grass fire.

11:19 – 11:23 a.m.:

From a vantage point at the top of the west exterior steps, Eric Harris and Dylan Klebold open fire. They are each strapped with two 9-mm semi-automatic weapons. Before entering the school, they kill student Rachel Scott and injure student Richard Castaldo.

Having just exited the school, students Daniel Rohrbough, Sean Graves, and Lance Kirklin are all shot. Klebold further pursues them and proceeds to shoot Rohrbough and Kirklin at close range; Daniel Rohrbough doesn’t survive.

Student Michael Johnson is hit but able to flee. Student Mark Taylor suffers an incapacitating gunshot wound and cannot move.

Witnesses recall one of the shooters yelling, “This is what we always wanted to do. This is awesome!”

Harris shoots student Anne Marie Hochhalter. Though Hochhalter lives, her mother tragically dies by suicide six months later (a gunshot to the head in the middle of a local pawn shop).

11:22 a.m.:

The community resource officer, Neil Gardner, is alerted of an emergency by the custodian. He activates his lights and siren.

11:24 a.m.:

As Harris and Klebold move through the school, they encounter teacher Patti Nielson and student Brian Anderson. The shooters fire and miss. Upon noticing Neil Gardner in the student parking lot, Harris fires in his direction. A shootout ensues.

Students in the cafeteria begin to panic and disperse. Teacher William “Dave” Sanders is said to be directing them to safety.

11:26 a.m.:

Harris and Klebold continue moving through the school, firing at students and teachers while laughing. Student Stephanie Munson is shot in the ankle but able to escape.

Klebold stumbles upon a student calling her mother. He doesn’t shoot.

Teacher Dave Sanders is shot. He crawls to the Science hallway where another teacher and students tend to his wounds. He eventually bleeds to death despite their best efforts.

11:27 a.m.:

In the library hallway, Harris and Klebold toss explosives and fire their guns randomly.

11:29 a.m.:

Eric Harris and Dylan Klebold enter the library where they kill ten of the 56 people inside: Kyle Velasquez, 16; Steven Curnow, 14; Cassie Bernall, 17; Isaiah Shoels, 18; Matthew Kechter, 16; Lauren Townsend, 18; John Tomlin, 17; Kelly Fleming, 16; Daniel Mauser, 15; and Corey DePooter, 17.

11:36 a.m.:

Harris and Klebold leave the library and travel toward the science area, all the while peering into classrooms and making eye contact with trembling students.

The two enter the cafeteria and begin tampering with the duffel-bag bombs.

They leave the cafeteria area.

They re-enter the library.

The next people they shoot are themselves.