Hijacked airplanes smashed into New York City's World Trade Center and the Pentagon in Washington, D.C., on Sept. 11, 2001, in terrorist attacks carried out by the Islamist group al-Qaida. The World Trade Center’s Twin Towers collapsed less than 90 minutes later.
Nearly 3,000 people were killed in the attacks.
A fourth airplane also headed to the U.S. capital crashed into a Pennsylvania field outside of Shanksville, when the passengers fought the hijackers in an attempt to regain control of the cockpit.
Nineteen hijackers died after they commandeered the planes to use as weapons.
The leader of al-Qaida, Osama bin Laden, had created the extremist organization in Afghanistan after the 1989 withdrawal of Soviet troops from the country. He opposed the presence of U.S. troops in Saudi Arabia and American policy in the Middle East among other grievances against the West. Bin Laden was killed during the Obama administration by a U.S. attack on the house where he was hiding in Pakistan.
The man accused of being the mastermind behind the attacks is Khalid Sheikh Mohammed, who is still being held at Guantanamo Bay with four others, charged with conspiracy, murder and terrorism. They face the death penalty. Jury selection for a trial before a military tribunal was to have begun in January but has been delayed because of the coronavirus pandemic and other issues.
Sources: NBC New York, The National 9/11 Pentagon Memorial, Friends of Flight 93
Design and development by Nelson Hsu
Editing by Noreen O'Donnell