On September 11, 2001 , terrorists hijacked 4 airplanes and crashed them into the two towers of the World Trade Center in New York and the Pentagon in Washington. The fourth jet crashed in Pennsylvania. About 3,000 people were killed and part of the Pentagon was destroyed. It was soon found out that Osama Bin Laden and his terrorist organization Al Qaeda had been behind the attacks. The planes left the airports on the morning of September 11. Their original destination was California , so they had tons of fuel on board. Sometime after take-off , the terrorists took over the planes. Some of them had pilot training. At 8:45 a.m. the first plane crashed into the north tower of the World Trade Center. 20 minutes later, the second plane hit the south tower.Flames and smoke came out of the towers and the people who were working there tried to escape. About an hour after the attack both towers collapsed. At about 9:40 a.m. a plane with 58 people on board crashed into the west side of the Pentagon, the country's military headquarters in Washington. A part of the building collapsed and about 200 people were killed. A fourth plane probably intended to crash into the White House or the Capitol, but a few passengers wanted to try to overcome the terrorists. The pilots lost control of the plane and it crashed into a field in Pennsylvania. After the attack on the USA, there was panic all over the country. The White House was evacuated and all air traffic over the continent was stopped. The stock exchange in New York stopped business and many tourist sights were closed down. A month after the attack, the government gave the police and the FBI more power to hunt terrorists. New safety checks at airports were introduced and airlines started checking the baggage of their passengers more carefully. The United States were convinced that Osama Bin Laden and his Al-Qaeda terrorist group were behind the attacks. In October, the U.S. attacked terrorist training camps in Afghanistan . The two Boeing 767s that took off from Boston hat a lot of fuel with them because they were traveling to Los Angeles. Each jet had about 90,000 liters of fuel—about 2 tanker trucks full. When the planes hit the towers they caused a massive fire that spread across many floors at the top of the buildings. Most likely,furniture, wood and paper in the offices began burning quickly , so that the fire could spread in a few seconds. The buildings did have an automatic sprinkler system, but this system was made to put out small fires. The fire caused temperatures of over 1,000 °C , so that even the steel constructions in the buildings became weaker and weaker. In the end, the top floors that remained undamaged were so heavy that the whole building collapsed. The World Trade Center, however,withstood collapse long enough to save thousands of lives. About 99 % of the people in the lower floors could get out of the buildings before they fell.