On 20th April 1999, in Littleton, Colorado, two high-school seniors, Eric Harris and Dylan Klebold, launched an assault on Columbine High School. Armed with guns, knives and bombs, the pair hoped to murder hundreds of students. In a 49-minute rampage, they killed twelve students and one teacher, before committing suicide. It was the worst school shooting in American history.

On 20 April 1999, in the small, suburban town of Littleton Colorado, two high-school pupils, Dylan Klebold, 17, and Eric Harris, 18, embarked on a shooting rampage at Columbine High School during the middle of the school day.Using all manner of weapons such as guns, knives, and a multitude of bombs, the two boys walked the hallways and killed. When the day was over, twelve students, one teacher and the two killers were dead.11:10 am Harris and Klebold arrived at the school in separate cars.
Klebold was armed with a 9-mm semi-automatic handgun and a sawn-off shotgun. Harris was armed with a 9-mm carbine rifle and a sawn-off shotgun. Both wore black trench coats to hide the weapons they were carrying and utility belts filled with ammunition.
They also carried knives and had a backpack and a duffel bag full of bombs.The pair parked separately in the junior and senior student parking spaces, with a clear view of the cafeteria. Some minutes later, they carried two 20-pound propane bombs, with timers set for 11:17am, in duffel bags and placed them near tables in the canteen. The boys then went back to their cars to wait for the explosion.Nothing happened. It is believed that if the bombs had exploded it is probable that all 488 students in the cafeteria would have been killed.

11:19 am the two pipe bombs that Klebold and Harris had set up in an open field, several blocks away, exploded. The boys had timed the explosion so that it would be a distraction for police officers and at the same time they started firing their first shots at students sitting outside the cafeteria.
Their first victim was 17-year-old Rachel Scott. Being only a few weeks before the seniors graduated, many of the other students did not realise what was truly happening and therefore did not immediately flee, thinking it was merely a boisterous but harmless ‘senior prank’.
Klebold and Harris walked through the halls, randomly taking aim at students and throwing their hand-made bombs. The boys entered the library and shouted for all the pupils to get up. When no-one did, they both started firing. Many of the pupils had hidden under the tables but the pair carried on shooting and continued their killing rampage from table to table. In total, they killed 10 students and injured 12 others.Klebold and Harris headed back downstairs and entered the cafeteria. Harris shot at one of the duffel bags they had placed there earlier, trying to get the 20-pound propane bomb to explode but it did not.
Klebold then threw another bomb at the duffel bag, which exploded and started a fire that triggered the sprinkler system.The boys continued to wander around the school, throwing bombs. They headed back to the library, which now housed nearly all of the uninjured students, and shot out of the windows toward the policemen and paramedics outside.12:05-12:08 pmKlebold and Harris went to the south side of the library and shot themselves in the head, ending the massacre that had lasted under an hour. In the end, one teacher and 12 students were killed and 24 other students were injured.