Principal DeAngelis addresses two thousand students at a prom-week assembly, calling the school "one large family" days before disaster.

Eric Harris and Dylan Klebold complete their final shift at Blackjack Pizza and spend the evening bowling with friends.

Eric and Dylan enter the school cafeteria just before "A" lunch begins and plant two large propane-tank bombs beneath tables.

Eric Harris opens fire from the top of exterior stairs, shooting and killing Rachel Scott and wounding Richard Castaldo.

Dave Sanders directs nearly five hundred cafeteria students up the stairs and down a hallway to safety from the shooters.

The two large propane-tank bombs planted in the cafeteria fail to detonate, sparing hundreds of students from near-certain death.

Eric and Dylan enter the school library, killing ten students and injuring twelve more before walking back out.

Gravely wounded Patrick Ireland spends hours crawling to a broken library window and falls onto a SWAT vehicle below.

Eric Harris and Dylan Klebold commit suicide in the school library forty-nine minutes after beginning the attack.

SWAT teams searching the building discover the bodies of Eric Harris and Dylan Klebold in the school library.

Dave Sanders bleeds out in a science classroom after waiting more than three hours for medical help that never arrives in time.

Investigators discover that Jefferson County law enforcement had prior knowledge of Eric Harris's threatening website before the attack.

Jefferson County officials hold a secret meeting to coordinate concealing their prior knowledge of Eric Harris's violent online threats.

Cassie Bernall's supposed martyrdom story is proven false, but her mother and publisher choose to keep the false account in their memoir.

Jefferson County settles a wrongful death lawsuit filed by Dave Sanders's daughter Angela, paying her $1.5 million.

On a Tuesday morning in April 1999, Eric Harris and Dylan Klebold carried out a planned attack on Columbine High School that began with planting bombs in the cafeteria and devolved into a shooting spree. The cafeteria bombs failed to detonate, preventing a far greater catastrophe, while teacher Dave Sanders died heroically directing students to safety before bleeding out in a locked classroom. The attack ended when both perpetrators killed themselves in the school library, leaving thirteen dead and dozens wounded. In the aftermath, investigators uncovered that local law enforcement had known about Eric Harris's threatening online posts before the attack. Jefferson County officials attempted to conceal this prior knowledge in a secret meeting, sparking years of lawsuits from victims' families. The consequences of the attack rippled outward for years, reshaping school safety policy and producing legal and personal reckonings for survivors and law enforcement alike.

The headline events of the Columbine attack and its lasting consequences.

Cassie Bernall's mother, Misty, arrives at the school perimeter and cannot locate her children at either evacuation rendezvous point.

Students in a locked classroom write "1 BLEEDING TO DEATH" on a whiteboard and display it in the window for rescuers.

Tom Klebold searches Dylan's bedroom, finds the trench coat missing, and calls 911 to report that Dylan may be involved.

Students hiding in locked Columbine classrooms watch delayed television coverage of the attack unfolding around them.

FBI Agent Dwayne Fuselier arrives at Columbine as the first federal agent on scene because his son attends the school.

Sheriff John Stone addresses the media and incorrectly states the death toll is nearly double the actual number of victims.

Bomb investigators discover the cafeteria propane bombs intact in the flooded commons and conclude the attack was primarily a failed bombing.

Detectives question Robyn Anderson about her role in purchasing three firearms for Eric and Dylan at the Tanner Gun Show.

Mark Manes, who sold the TEC-9 to Eric and Dylan, is arrested and later sentenced to nine years in prison.

A mass candlelight vigil draws more than 70,000 people to a shopping center near Clement Park, far exceeding organizers' expectations.

A Chicago carpenter plants fifteen wooden crosses on Rebel Hill, including two for Eric and Dylan, sparking fierce community controversy.

Eric Harris and Dylan Klebold are arrested after a sheriff's deputy watches them break into a van on a country road.

Patrick Ireland walks out of Craig Hospital on a crutch after nearly ten weeks of rehabilitation from his gunshot wound.

Columbine High School reopens with a "Take Back the School" rally, with Patrick Ireland leading the student body inside the building.

Fifteen families file wrongful death and negligence lawsuits against the Jefferson County sheriff's department over the Columbine attack.

As the shooting unfolded, families like the Bernalls and Klebolds scrambled to locate their children while law enforcement struggled to contain the crisis and communicate accurate information to a watching nation. In the immediate aftermath, Sheriff Stone gave incorrect statements to the press and investigators began piecing together how the killers had obtained their weapons, leading to the arrest of gun dealer Mark Manes. The Columbine community gathered in enormous public vigils to grieve collectively, while controversies erupted over symbolic gestures like the carpenter's crosses planted on Rebel Hill above the school. Survivors including Patrick Ireland underwent long and difficult rehabilitation, and the school worked to reclaim its identity through a carefully staged reopening rally. The legal process ground forward slowly, with fifteen families filing wrongful death suits against Jefferson County in an effort to compel disclosure of what officials had known before the attack.

The survivors, witnesses, and community in the hours and weeks following the shooting.

Eric Harris tells classmate Brooks Brown to go home moments before entering the school to begin the attack.

Dylan Klebold enters the crowded cafeteria during the attack, raises his weapon toward students, but fails to fire and walks out.

Art teacher Patti Nielson approaches Eric Harris to stop what she assumes is a student prank and is shot at through glass doors.

Eric Harris shoots Anne Marie Hochhalter twice in the back as she attempts to flee, rupturing her spinal cord.

Police enter the Harris home over the family's objections and find a page from The Anarchist Cookbook in Eric's basement bedroom.

Principal DeAngelis encounters students walking unknowingly toward the shooters and leads them to safety inside the locked school gym.

FBI Agent Fuselier determines the Columbine crisis is not a hostage standoff and that a fundamentally different law enforcement strategy is needed.

Agent Fuselier watches the Basement Tapes repeatedly in the weeks after the attack, methodically searching for the motive behind the massacre.

Agent Fuselier reads Eric Harris's journal entries and formally concludes that Eric is a clinical psychopath rather than a person who is insane.

The FBI holds a major summit on school shooters and expert colleagues confirm Fuselier's psychopathy assessment of Eric Harris.

Dylan Klebold submits a story vividly describing a mass killing spree to his creative writing teacher, who contacts Dylan's parents in alarm.

The Active Shooter Protocol is adopted nationwide, requiring officers to storm buildings and confront active shooters rather than establish a perimeter.

A released search warrant proves conclusively that Jefferson County officials knew about Eric Harris's threatening website from the very start of the attack.

Eric and Dylan enter a "quiet period" after leaving the library, roaming the school but failing to shoot students they encounter.

The permanent Columbine memorial is unveiled years after the attack, with thirteen doves released for the victims followed by two hundred more.

Several pivotal turning points shaped both the attack itself and its long aftermath, beginning with Eric Harris's chilling warning to Brooks Brown moments before the shooting started and Dylan Klebold's repeated failures of nerve during the attack. Principal DeAngelis made split-second decisions that saved lives, while law enforcement's flawed response would later be identified as a direct cause of Dave Sanders's death. FBI Agent Dwayne Fuselier's sustained analysis of the killers' recordings and journals led him to formally conclude that Eric Harris was a clinical psychopath, a finding that transformed expert understanding of the attack's roots. The failure of local law enforcement to act on prior knowledge of Harris's violent online presence became the central scandal of the investigation, only fully exposed years later through a court-ordered search warrant. Institutional change ultimately followed, as the Active Shooter Protocol overhauled police response to school shootings nationwide and a permanent memorial finally gave the community a place to grieve.

The key decisions, discoveries, and turning points that define the full story of Columbine.