The first 9/11 demolition claim appeared online within six hours
Less than six hours after the attacks of September 11, a chatroom post suggested the towers had been brought down by controlled demolition. That idea became the best known of many 9/11 conspiracy theories. Government inquiries, engineers and independent investigators have examined these claims and rejected them.
The established account is that al-Qaeda hijackers flew two airliners into the World Trade Center towers and a third into the Pentagon, while a fourth plane came down in a field near Shanksville, Pennsylvania, after passengers and crew fought to retake it. Impact damage combined with the fires that followed brought the towers down. Conspiracy theories variously claim controlled demolition, a missile strike on the Pentagon, remotely piloted jets, a deliberate military stand-down or officials who knew in advance and let it happen.
Investigators have tested those claims directly. The National Institute of Standards and Technology and the magazine Popular Mechanics both examined them and found no support, and the 9/11 Commission and most civil engineers accept that high-speed jet impacts plus fire, not explosives, caused the collapses. Purdue University scientists reached the same view. The Commission did find genuine failures: warnings about al-Qaeda went unheeded because agencies did not share information, and it blamed both the Clinton and Bush administrations for a failure of imagination.
Elaborate versions first gained traction in Europe. A week after the attacks Le Monde published an inside-job thesis by a French state researcher, and six months later Thierry Meyssan's L'Effroyable Imposture topped the French bestseller list, becoming a founding text of so-called trutherism. Some claims were outright bigotry, such as the false rumour that no Jews died in the attacks. In the United States, media first reacted with bafflement, and President Bush denounced such theories at the United Nations in November 2001.
By 2004 the theories were spreading in America too, which reporters linked to anger over the Iraq War rather than to new evidence. Having begun mainly on the left, the movement later drew in anti-government voices from the right. Psychologists caution against smugness, though: one study found that the ability to tell verified conspiracies from unverified ones tracked reasoning skill better than simply rejecting every conspiracy claim.
Source: 9/11 conspiracy theories
