BBC News has put together an overview of the five most common conspiracy theories circulating in the internet community:

1. Why was the world's most powerful air force unable to stop any of the four hijacked planes?

Conspiracy theorists claim: Then-Vice President Dick Cheney ordered the military to withdraw and not attack the plane.

The official report states: This was a highly unusual violent multiple hijacking on board an aircraft in which the aircraft's precise location transmitter was disabled or altered. Apart from that, routine training was also held at US Air Force Headquarters that day. Air traffic controller Colin Scoggins was in constant contact with the military and testified that he saw “no response.” However, there was confusion and a lack of communication between civilian and military air traffic controllers. Military equipment was also outdated and designed to monitor what was happening in the oceans to deal with Cold War threats.

2. Why did the “twins” collapse so quickly and straight after a multi-story fire that lasted only an hour or two?

Conspiracy theorists claim: The twins destroyed controlled destruction. Theories refer to the speed of the collapse (around ten seconds), the relatively short duration of the fire (56 minutes at WTC2 and 102 minutes at WTC1), reports of the sound of an explosion immediately before the collapse, or a violent explosion in part of the building. windows on a row of floors before collapsing.

The official report states: An extensive investigation by the American National Institute of Standards and Technology (NIST) concluded that the planes had clipped and damaged support columns and fire protection systems. About 38,000 liters of jet fuel spilled onto several floors and sparked a large fire. Temperatures reaching 1,000 degrees Celsius caused the floor to collapse and the barrier pillars to buckle, producing a sound similar to an explosion. The weight of the sinking floor creates a load that far exceeds what the support beams are designed for. As the floor collapsed, window shards flew. Controlled demolition is always carried out from below, whereas in this case the collapse started from above. No evidence was found to support the ready-made explosion theory, although the debris was manually searched. There were also no signs of pre-cutting of walls or columns, which is usually done in controlled demolition.

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3. How could an amateur pilot fly a commercial airliner through complex maneuvers and crash it into the Pentagon 78 minutes after the first report of a possible hijacking?

Conspiracy theorists claim: The Pentagon was not hit by a Boeing 757, but by a rocket, small plane or drone. Since evidence emerged that American Airlines Flight 77 did indeed crash into the building, conspiracy theorists have focused on the complicated approach maneuver. They now claim that the plane was not under the control of al-Qaeda, but rather the Pentagon itself.

The official report states: Debris, including black boxes, was collected at the scene and examined by the FBI. The remains of passengers and crew were also found and positively identified with the help of DNA. Witnesses also saw a plane crash into the Pentagon.

4. Why is the crash site in Shanksville, Pennsylvania (where the plane allegedly bound for the White House with the hijackers crashed) so small and with no visible debris?

Conspiracy theorists claim: United Airlines Flight 93 was shot down by a missile and the plane disintegrated in mid-air, scattering debris over a wide area.

The official report states: There are clear photos of the wreckage at the scene and audio recordings from the cockpit that prove that the passengers resisted the hijackers and then deliberately crashed the plane. Initial theories that debris was strewn over a wide area have been proven wrong. In reality, the wind only blew lighter debris, such as paper or insulation material, about a mile and a half away.

5. How could a skyscraper (World Trade Center building number 7) that was not hit by a plane collapse so quickly and symmetrically when no other steel structure skyscraper collapsed due to fire?

Conspiracy theorists claim: The WTC7 building was destroyed in a controlled demolition using explosives and incendiary materials. Initial interest was sparked by the word “pull” used by owner Larry Silverstein in a TV interview. But he was actually talking about tearing down the firehouse, not destroying the building. The English phrase “pull it” he used was not used by demolition crews to detonate explosives, as conspiracy theorists interpret it. Attention was also drawn to the speed of collapse which reached 2.25 seconds
almost free fall. Conspiracy theorists claim that only explosives could collapse a building so quickly and symmetrically. Some scientists skeptical of the official report have examined dust samples from Ground Zero and say they have found thermal materials that react violently when heated. Therefore they claim that not only inside WTC7, but also in the “twins” there are tons of thermite and conventional explosives.