They wouldn't do that, would they? Lots of good stuff in this article

http://onlinejournal.com/artman/publish/article_277.shtml

The sponsorship of terrorism by western governments, targeting their own populations, has been a taboo subject. Although major scandals have received cursory coverage in the media, the subject has been allowed to immediately disappear without discussion or investigation. Therefore the appearance this year of two major studies of this subject is a welcome breakthrough, and provides essential reading for anyone struggling to understand the events of September 11, 2001 and the post September 11 world.

The studies are complementary. NATO's Secret Armies, Operation Gladio and Terrorism in Western Europe by Daniele Ganser concerns terrorism sponsored by American and British intelligence in Western Europe and Turkey between the end of World War II and 1985. The War on Truth, 9/11, Disinformation, and the Anatomy of Terrorism by Nafeez Mosaddeq Ahmed chronicles the cultivation and sponsorship of militant Islamic terrorism by the intelligence services of the United States, Britain and Russia from 1979 to the present. Both studies are models of scholarship -- meticulously documented and carefully reasoned -- but the world they reveal will boggle the mind of the most wild-eyed conspiracy theorist.
...
Ahmed points out that the responsible authorities at the Pentagon and the Federal Aviation Administration have produced several profoundly contradictory accounts of their own actions on that day -- each subsequent story seemingly an attempt to remedy the shortcomings of a previous one. And still no remotely satisfactory account of the failure to intercept even one of the four hijacked airliners has been produced. Under ordinary circumstances, interception of wayward aircraft by military fighters would have been absolutely routine; such interceptions occurred at least 56 times in the calendar year prior to September 11, 2001. Ahmed points out that the attacks were allowed to proceed "entirely unhindered for over one and one half hours in the most restricted airspace in the world." He finds the idea that this was due to negligence beyond belief. Instead he argues that there must have been a deliberate stand-down of the air defence system managed by senior national security officials including the vice president and the secretary of defense.