12.07am: First reports emerge of the carnage. Jefferson County police claim two explosions also heard and fire started at rear of main building. More police arrive and ambulances start ferrying injured. Witnesses report "men in black trench coats" opening fire and hurling home-made pipe bombs.
12.17pm: Reports claim the two gunmen, dressed in black and wearing masks, are students at the school. Nearby schools put on a "lockdown" status, with students prohibited from entering or leaving.
12.36pm: Witnesses report men armed with shotguns or sub-machine-guns roaming through the school throwing fire bombs.
12.56pm: Police in camouflage gear arrive.
1.18pm: School now surrounded by about 100 armed police. Local hospitals say they are treating five injured.
1.24pm: Pupils say gunmen belong to a gang calling themselves the Black Trenchcoat Mafia - a group of around 10 anti-social student misfits who wear dark clothes, camouflage fatigues and sunglasses. Dave Hnida, school team doctor, said they were devotees of the controversial rock star Marilyn Manson - a cult heavy metal star popular with rebellious American teenagers. The group is suspected of recent daubings of swastikas on school lockers.
1.38pm: Up to 20 students flee to safety with their hands in the air. Police Swat team storms the building. Reported number of injured rises to 11. Wounded male student dangles from second floor window and is rescued by police.
2.15pm: Three men dressed in black flee the building, to be arrested by police in fields. Police say they were former students who were associates of the two gunmen. Number of injured rises to 16, including a girl who suffered nine gunshot wounds to the chest. A second girl had a wound to the chest, a boy had a wound in the back, and another youth had three gunshot wounds in the chest and arms.
2.30pm: Police move armoured cars and fire trucks up to school entrances to help to protect the evacuation of the wounded. Four squads of Swat officers search the building. More students flee. They say the massacre centres on the library. One group of students trapped in choir room call police on mobile phones. Another class shelters in biology laboratory until rescued by Swat team.
4pm: Police say two suspects killed themselves and were discovered among numerous dead in the library. Sheriff John Stone said up to 25 staff and pupils may be killed and up to 18 injured. Swat teams continue a sweep of the school buildings and bomb disposal experts are drafted in.
4.48pm: Police say suspects had shot themselves. Four home-made pipe bombs discovered in building and a fifth bomb discovered at the home of one of the dead gunmen.Reuse content