The record
On September 11, 2001, nearly 3,000 people were killed when hijackers flew planes into the World Trade Center in New York, the Pentagon and a field in Pennsylvania. The 9/11 Commission, set up by Congress, laid out the plot by al Qaeda in its 2004 report. This page does not question that the attacks happened or who carried them out. It looks at the questions people still raise, starting with the one that has the most physical detail behind it.
World Trade Center 7 was a 47-story office building across the street from the North Tower. No plane hit it. Debris from the North Tower's collapse set it on fire, the fires burned without water to fight them for about seven hours, and the building fell at 5:20 p.m. Video shows it coming down straight and fast, which led many people to ask whether it was taken down on purpose.
The National Institute of Standards and Technology (NIST) studied the collapse and released its final report in November 2008. It found that heat made steel floor beams expand and push a girder off its seat at a key column, Column 79. That set off a chain of failures inside the building before the outside walls came down. NIST called it the first known case of a tall building collapsing mainly because of fire. After outside critics pointed it out, NIST also confirmed that for about 2.25 seconds the building fell at the speed of free fall.
A study at the University of Alaska Fairbanks, led by engineering professor Leroy Hulsey and paid for by the group Architects and Engineers for 9/11 Truth, released a final report in March 2020. It said fire could not explain the collapse and that the building came down only because nearly every column failed at once. NIST considered and rejected explosives: it found no blast sounds loud enough to cut columns on the recordings and judged thermite highly unlikely.
Other common claims have official answers on record. Reports of unusual stock trading on airline shares just before the attacks were checked by the 9/11 Commission, which found that each trade had an innocent explanation; for example, one US investor with no link to al Qaeda bought most of the United Airlines put options as part of a wider trading plan. Security camera frames from the Pentagon attack were released in 2006.