Conspiracy theories
Main article: 9/11 conspiracy theories
Proponents of conspiracy theories have suggested that individuals inside the United States possessed detailed information about the attacks and deliberately chose not to prevent them, or that individuals outside of al-Qaeda planned, carried out, or assisted in the attacks. Some conspiracy theorists claim the World Trade Center did not collapse because of the crashing planes but was demolished through the use of explosives.[174] This controlled demolition hypothesis is rejected by the National Institute of Standards and Technology and by the American Society of Civil Engineers, who, after their research, both concluded that the impacts of jets at high speeds in combination with subsequent fires caused the collapse of both Twin Towers