There can no longer be any doubt that the Cheney / Bush administration not only lied to the American people about WMD's and Torture but lied to and obstructed the 9/11 commission during its investigation of 9/11.
Tom Kean and Lee Hamilton, the two chairmen of the 9/11 commission, wrote a NY Times editorial on January 2, 2008 that said the CIA or the White House obstructed their investigation ~ and it doesn't get more obvious than this.
" MORE than five years ago, Congress and President Bush created the 9/11 commission. The goal was to provide the American people with the fullest possible account of the “facts and circumstances relating to the terrorist attacks of Sept. 11, 2001” ~ and to offer recommendations to prevent future attacks. Soon after its creation, the president’s chief of staff directed all executive branch agencies to cooperate with the commission.
The commission’s mandate was sweeping and it explicitly included the intelligence agencies. But the recent revelations that the C.I.A. destroyed videotaped interrogations of Qaeda operatives leads us to conclude that the agency failed to respond to our lawful requests for information about the 9/11 plot. Those who knew about those videotapes ~ and did not tell us about them ~ obstructed our investigation."