Not since the JFK assassination has there been a national tragedy so heavily imprinted in American minds — or that has given rise to quite as many alternative explanations. While videos and photographs of the two planes striking the World Trade Center towers are famous around the world, the sheer profusion of documentary evidence has only provided even more fodder for conspiracy theories.
A May 2006 Zogby poll found that 42% of Americans believed that the government and the 9/11 commission “concealed or refused to investigate critical evidence that contradicts their official explanation of the September 11th attacks.” Why had the military failed to intercept the hijacked planes? Had the government issued a “stand down” order, to minimize interference with a secret plan to destroy the buildings and blame it on Islamic terrorists? In 2005, Popular Mechanics published a massive investigation of similar claims and responses to them. The reporting team found that the North American Aerospace Defense Command (NORAD) did not have a history of having fighter jets prepped and ready to intercept aircraft that had gone off route. And while the team found no evidence that the government had planned the attacks, lack of proof has rarely stopped conspiracy theorists before.
Source : time.com