Many of the conspiracy theories and allegations were investigated by a team of nine researchers and reporters assembled by Popular Mechanics magazine, who consulted 70 professionals in fields including aviation, engineering and the military. [1] The magazine stated that the team was able to "debunk" each of theories "with hard evidence and a healthy dose of common sense". It also concluded that "a few theories are based on something as innocent as a reporting error on that chaotic day. Others are the byproducts of cynical imaginations that aim to inject suspicion and animosity into public debate."

An increasing number of commentators (In particular Michael Ruppert of From the Wilderness Publications) have been speculating on the connections between the 'catalyzing' events of September 11th relating to the war on terrorism, and the incoming reduction in global production of oil, a theory termed Peak Oil.

barred from certain "key intelligence" documents classified as the government's most sensitive intelligence documents by the Bush Administration

The Yellowcake forgery forgery after they were used as evidence to justify the invasion of Iraq. Whether or not any U.K. and U.S. officials knew that the documents were not authentic is still being debated.

Critics of these theories point out, however, that most believe that such theories are political speculation with no evidence or credible sources that any person in authority had knowledge of the attacks, would desire to kill thousands of Americans to make a political point, or could or would conspire with Islamic terrorists.

The plane that crashed into the Pentagon hit a less populated section of the building that had been cleared for renovation well in advance of the September 11, 2001. The Pentagon renovation project had been planned for over a decade prior to the attacks. As a result, the vast majority of the offices in the section of the Pentagon damaged by the plane crash were empty on the day of the attack and had been empty for some time before the attack. Nevertheless, the attack caused 200 casualties in the Pentagon and on the ground (124 killed and 76 injured), not including those that died in the plane.[2]

• 3-Year Federal Study of 9/11 Urges Safer Skyscraper Rules, New York Times, June 22, 2005

The vast majority of people dismiss such claims as outlandish and objectionable. They are as outlandish as the Apollo moon landing hoax accusations that formerly provided U.S. government conspiracy theorists with ammunition and the Flat Earth Society members who refused to listen to reason. Because many of the conspiracy theorists oppose the policies and officeholders of the U.S. Administration, many believe that those who promote such theories are doing so for political reasons. And because this conpiracy involves enourmous trajedy, death and destruction, many people object to promoting such outlandish beliefs and accusations for what they believe are political reasons.

Proponents of the domestic complicity conspiracy theory often point to historical precedents, in which governments have allegedly planned to use tragedy in order to gain support for unpopular policies. Opponents believe that there is no rational basis for such "historical precedents" and that such analogies are not proximately related to the U.S. Government or any 9/11 events.

A few believe that the WTC towers did not collapse in the manner described in the government's investigative report. The generally accepted scientific evidence describes the collapse of the towers.

This phenomenon involving such beliefs is frequently viewed as a conspiracy theory wherein the common understanding of the theory's proponents is that they have substituted zeal and political beliefs for knowledge and logic.