It was just before lunch break at Columbine high school, a good school in Littleton, a prosperous suburb of Denver.
Like thousands of other secondary schools where yesterday was just another Tuesday, its students were sitting in class and beginning to dream of summer.
Denver has its share of urban violence but Littleton, a town of 35,000 people close to the Rocky mountains, is a place of large homes and wide driveways, where teenagers drive to schools in their own cars.
But for Littleton, everything changed at 11.30 a.m. when shots rang out, first in the canteen, then in the long hallways, and Columbine high was pitched into the kind of notoriety that every school in the US fears. The exact course of the events that have catapulted this Colorado town into a very special league of American infamy occupied by places such as Jonesboro, Arkansas, where two boys killed a teacher and four girls in March 1998, is still not clear. The final death toll has yet to be determined.
But as the screaming and panicking staff and pupils rushed from the well-appointed modern school buildings they told a story that is now too shockingly common in American schools to be called a random catastrophe.
It appears that this was a massacre coldly planned by teenage boys and it was done from within. The young gunmen wore long black trench coats, and black ski masks. A witness claimed that one of them carried an Uzi submachine gun. Under their coats they are reported to have hidden pipe bombs.
They had style, they had guns, and they were probably barely old enough to shave. According to witnesses, the gunmen were pupils who fired on their fellows. Everyone seemed to know them, or at least to know of them. Some called them the "trench coat mafia" and said that they were an anti-social high school clique.
Others said they were a gay gang, who wore the trenchcoats to school as a kind of uniform, and painted their faces with make-up and lipstick. "They were jerks. They are really strange," said one pupil. "But I've never seen them do anything violent."
When the mayhem began late yesterday morning, they started shooting indiscriminately. In the school cafeteria, they pointed their guns at anything that moved. Bullets ricocheted from wall to wall in the corridors lined with lockers. Someone ran screaming into the school library, shouting at those inside to get down.
In classes around the school, staff and pupils crouched under tables and desks, or ran for what they hoped would be safety.
In the canteen, a woman helper grabbed six students and together they locked themselves into a toilet.
In other rooms, startled groups barricaded themselves inside, terrified of the noise and unknown horror outside.
In the far-flung corners of the school, people heard the shots with disbelief. Within an hour, eight injured students were being ferried to local hospitals with horrible injuries.
One girl had nine gunshot wounds in her chest. Later, the numbers of wounded mounted inexorably and grimly and the first reports of dead bodies inside the school began to be rumoured.
At the same time that the first wounded pupils were being shepherded to safety by the first emergency crews to reach the scene, the first television companies arrived. From that moment, a local horror in an obscure suburb mushroomed to become a world news event.
Less than an hour after the first shots had rung out, CNN halted its coverage of the Kosovo conflict to bring uninterrupted live coverage of the Denver drama.
For connoisseurs of the modern news creation process, the continuing siege at Columbine high school has produced some extraordinary counterpoints.
Besieged groups of staff and students, trapped inside the school, watched their own danger unfolding on television from their locked classrooms.
A young girl, weeping from fear, was interviewed live on air on her mobile as she fled from the scene.
Incredibly, there was even a live interview with a teenager who had his mobile phone with him in a locked room inside the school.
A hoaxer got in on the act, trying to claim that the shootings were the fault of a controversial radio personality, Howard Stern, before this caller found himself cut off.
Even President Clinton pitched in, breaking into the coverage to say he hoped that Americans were praying for the hostages and their families.
"We'll wait for events to unfold, and then there'll be more to say," Mr Clinton announced in his unscheduled soundbite. And with that, the nation's president, and perhaps even the gunmen with their hostages, went back to watch the television coverage of the latest unbelievable horror from the US heartland.