Wednesday, April 21, 1999 Published at 21:58 GMT 22:58 UK
Timetable of terror
Police escourt pupils from the school
The massacre at the Columbine High School in the Denver suburb of Littleton - by far the worst in a series of school shootings in the US - began around mid-morning.
At 1130 local time (1830 BST) reports began to come in of two or three masked gunmen entering the school, which has about 1,800 students.
The two gunmen, wearing masks and black trenchcoats, began firing in the cafeteria and library. Later reports suggested they picked on ethnic minorities and "jocks", a slang term for athletic types.
Students hide under tables and in cupboards while others barricade themselves in a biology laboratory.
At noon police Swat teams arrive on the scene and find several explosive devices around the school. They initially believed they were dealing with a hostage-taking situation.
An hour after the shooting began, television cameramen were on the scene, relaying images nationwide and then worldwide.
Many of the survivors will take years to recover
Casualties began arriving at two local hospitals. Five people, suffering from serious gunshot wounds were taken to the Swedish Medical Centre in Denver.
Parents wandered about at the nearby Clement Park hospital, trying to find their children while students stood shaking and crying.
Police helicopters whirled overhead and hundreds of police officers patrolled the school as confusion reigned.
At about 1300 local time (2015 BST) frightened students, their hands in the air, were evacuated and frisked by police.
At around 1330, an armoured car was brought to the main school entrance for cover as dozens more students fled the building.
Around 1400, three youths wearing black clothes - but not trenchcoats - were apprehended by armed police in a field near the school. The trio were later described as "friends of the gunmen".
Some time in the afternoon police raid the homes of the two suspects and discover more pipe bombs.
Steve Davis, a spokesman for Jefferson County Sheriff's department, announced police were looking for two suspects, but said it was not clear where they were in the building.
At around 1600 police found two suspects shot
dead in the library. Their wounds were apparently self-inflicted.
At around the same time Sheriff John Stone said the death toll appeared to be up to 25.
At around 1615 the Swat team began a slow sweep of the building looking for survivors.
At 1630 the Swat team declares the school safe.
But at 1815 the authorities find an explosive device in a car in the car park. The campus is sealed off with
By 2200 the bodies remain in situ because of fears of booby traps inside the school.