Saturday marks 20 years since 19 al Qaeda terrorists hijacked four commercial airplanes on Sept. 11, 2001, leading to the deaths of nearly 3,000 people and a major reshaping of American life.
The FBI reported Sept. 11 as the deadliest terrorist attack in U.S. history. The sites remain the largest crime scenes in the agency's history.
At about 8:45 a.m. on Sept. 11, terrorists crashed a Boeing 767 with 20,000 gallons of jet fuel into the 110-story north tower of the World Trade Center in New York City. A second Boeing 767 crashed into the south tower near the 60th floor about 17 minutes later.
At 9:45 a.m., a Boeing 757 crashed into the west side of the Pentagon in Washington.
At 10:10 a.m., a fourth plane — United Flight 93 — crashed into a field near Shanksville, Pennsylvania, after passengers and flight attendants, aware of the attacks in New York and Washington through cell phone calls, fought the hijackers.
The WTC's south tower collapsed about an hour after being hit. The north tower collapsed less than 30 minutes later.
There were about 185 people killed at the Pentagon, 44 aboard Flight 93, and about 2,750 people died in New York, including more than 400 firefighters and police officers. All 19 terrorists died.