Eric and Dylan had arrived in the school carpark and entered through the back cafeteria door. They were wearing the long black trench coats that were the trademark of the small clique of students, "The

"Trench Coat Mafia" (AP)

Trench Coat Mafia", of which they were peripheral members. It was not until the teenagers began firing, from the semi-automatic weapons they had carried, concealed under their coats, that students and staff who filled the cafeteria realised that something was wrong.

Teacher and Coach, Dave Sanders was shot twice as he attempted to herd as many students as possible out of the cafeteria and away to safety. His quick thinking and bravery saved the lives of many students but, unfortunately, at the cost of his own. By the time he was able to get out of the cafeteria he was bleeding heavily from gunshot wounds to his chest and shoulders and was already coughing up blood. Students attempted to stem the blood flow from Sanders's wounds, as they cowered behind desks and tables in terror, but he died shortly after rescue teams finally reached him.

Students fleeing the high school (AP)

As Harris and Klebold marched through the building, heading toward the library, students and teachers fled. Some hid in bathrooms, some in storage rooms; others had no more protection than the tables under which they had crawled. From outside the building, police and SWAT teams who had begun to arrive could hear the sounds of gunfire and explosions. Students poured out of doors and windows, crying, screaming, some with injuries. They fled as far from the building as they could go. Ambulance workers and police tried to keep track of them as they made their escape. The injured were tended to as the SWAT teams tentatively entered the building, not knowing what was in store for them.

Homemade bombs and explosive devices were found planted around the building. The first priority was to evacuate the school before any of them could detonate. As the police scoured the ground floor looking for bombs, victims and the persons responsible for the carnage, Harris and Klebold were continuing their "mission" on the second floor, hunting down any stray students who were hiding in classrooms. In the library, students, who had only moments before been studying, were shot down in a blaze of gunfire. Several survivors later reported that Harris and Klebold were smiling and laughing as they shot their fellow students. The last shots heard were at 12.30pm when Harris and Klebold took their own lives.

SWAT teams still did not know how many shooters there were, whether they were dead, or quietly waiting to ambush the police. As each bomb was located, it had to be defused. Students, injured and frantic with fear had to be escorted from the building to ensure their safety. Each one was also searched for bombs and weapons. It was not until 4.00pm that police declared the building secure. All survivors had been evacuated. The bodies of the two killers were found with their guns in their hands and explosive devices hidden under their coats. Police were able to announce the death toll, including the shooters, as being 15.

All of the six district hospitals had been put on alert as soon as news of the shooting had been reported by the school's security guard at 11.35. They had swung automatically into emergency procedures. By 12.00pm, when the first of the victims began to arrive, they were ready for anything. Twenty- five people were admitted for treatment. Twenty-three with bullet wounds. Three were in a critical condition.

Woman embraces her daughter (AP)

Terrified parents flocked to the school, watching helplessly as students ran from the building, hoping to catch a glimpse of their sons and daughters. In the midst of the chaos, someone began to organize a list of all known survivors. Parents read through the lists, searching for the name of their child. Many would have to wait a long and agonizing time before word of their child would bring relief. For others, the relief would never come.

When the sun set that night, it was on a different Littleton. Everyone in the town was to be affected by the tragic and frightening events of Tuesday, 20 April 1999. They were no longer innocents. No longer could they live secure in the knowledge that such things could never happen to them. It had happened. The next few months would bring the painful grief, self-recrimination and blame that is a natural process of coming to terms with such a violent and tragic event.