The Shenon article is here.
In the interview for the documentary, Clarke offers an incendiary theory that, if true, would rewrite the history of the 9/11 attacks, suggesting that the CIA intentionally withheld information from the White House and FBI in 2000 and 2001 that two Saudi-born terrorists were on U.S. soil – terrorists who went on to become suicide hijackers on 9/11.
But there is plenty of reason to doubt it. For one thing, Clarke himself admits that it's only a theory:
Clarke speculates – and readily admits he cannot prove -- that the CIA withheld the information because the agency had been trying to recruit the terrorists, while they were living in southern California under their own names, to work as CIA agents inside Al Qaeda.
For another, it's already been investigated, as the theory is nothing new:
The 9/11 Commission investigated widespread rumors in the intelligence community that the CIA tried to recruit the two terrorists—Clarke was not the first to suggest it—but the investigation revealed no evidence to support the rumors. The commission said in its final report that "it appears that no one informed higher levels of management in either the FBI or CIA" about the two terrorists.
Tenet denies it although that is unsurprising.
Also note that the producers of the new documentary (the same guys responsible for the Troofer-Lite 9-11 Press for Truth sat on this "explosive" theory for almost two years:
He did not reply to requests from The Daily Beast to expand on his comments or to explain why he has not repeated them publicly since the 2009 interview. The documentary’s producers, FF4 Films, said they had been in contact with Clarke this month and that he stood by his remarks in the broadcast.
Update: YouTube Video of the interview: