Pew report on Muslims in the US. Key paragraph:
Relatively few Muslim Americans believe the U.S.-led war on terror is a sincere effort to reduce terrorism, and many doubt that Arabs were responsible for the 9/11 attacks. Just 40% of Muslim Americans say groups of Arabs carried out those attacks. Read the rest and pull up the PDF of the whole report.
That is actually quite a frightening statement. 40% of Muslims in the US are truthers. That is not a good sign.