Wednesday, April 21, 1999 Published at 02:08 GMT 03:08 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 1115 local time (1815 BST) reports began to come in of two or three masked gunmen entering the school, which has about 2,000 students.
The two gunmen began firing in the cafeteria and library. Later reports suggested they picked on ethnic minorities and "jocks", a slang term for athletic types.
Swat teams, in camouflage gear, were on the scene less than an hour after the shooting began. 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 (2000 BST) the first Swat team entered the building, still unsure whether the gunmen were alive and in the building.
Up to 20 students fled to safety.
Frightened students, their hands in the air, were evacuated and frisked by police.
At around 1330 (2030 BST) an armoured car was brought to the main school entrance for cover as dozens more students fled the building.
Around 1400 (2100 BST), 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".
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 (2300 BST) 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 1630 (2330 BST) the Swat team began a slow sweep of the building looking for survivors.
1815 (0115 BST) Authorities find an explosive device in a car in the
school parking lot.
2230 (0530 BST) Bomb on a timer blows up. No-one injured.
Wednesday morning - Police revise death toll to 15, based on a
count of bodies.