Q: what is the 9/11 conspiracy?
A: Since the events of 9/11, a variety of conspiracy theories have challenged the official account of events that day. The content of the challenges typically include suggestions that individuals in the government of the United States knew of the impending attacks and refused to act on that knowledge, or even that they took active part in the attacks. Conspiracy theorists have claimed that the collapse of the World Trade Center was caused by demolition charges or explosives placed in the buildings. Some also contend that a commercial airliner did not crash into the Pentagon, and that United Airlines Flight 93 was shot down. A majority of structural engineers do not support the controlled demolition hypothesis and U.S. officials insist that only al-Qaeda was involved in the attacks.