Was it planned?
Some famous conspiracy theories rely on anti-Semitic tropes, such as the attacks being orchestrated by Israel. Many claim that because "jet fuel can't melt steel beams," the Twin Towers must have been brought down by controlled demolition from bombs planted before the planes hit. (A 2006 NOVA documentary debunked these claims. It is, in fact, quite possible for the columns holding up skyscrapers to fail catastrophically when exposed to fires burning on multiple floors.)
Other claims are refuted by simple logic: If a hijacked airplane did not crash into the Pentagon, as is often claimed, then where is Flight 77 and its passengers? In many conspiracy theories, bureaucratic incompetence is often mistaken for conspiracy. Our government is so efficient, knowledgeable and capable — so the reasoning goes — that it could not possibly have botched the job so badly in detecting the plot ahead of time or responding to the attacks.
