And accused two of them – the King’s nephew and the Pakistani air force chief – of having advance knowledge of the 9/11 attacks.

The scenario seems plausible, though as bamage points out the cited material from Posner contains no substantiation aside from "I reported on this in my book, too."

The thing I have a hard time believing is that Posner's scenario would lead the CIA to hide the tapes from Congress. There were a bunch of Qaeda symps in Saudi Arabia and Pakistan? And some of them were in government? This is a surprise that needs to be hidden from Congressional Democrats?

As for knowing about the September 11th attacks in advance, look, I hate to say this but anyone who did not know that al Qaeda was, in general, trying to fly fuel-laden airplanes into the World Trade Center was willfully ignorant, and it didn't take special knowledge or genius intelligence to observe that by 2001 it had been longer than usual since the last time al Qaeda had been caught.

And by "anyone" I don't mean anyone in the Bush administration, or people with top-secret security clearances. I mean anyone — you, me, everyone in America who could read the New York Times, which quietly covered enough of the covert war against al Qaeda to convey everything one needed to know except the names and dates of the next attack.

So why should "so and so knew about 9/11 in advance" be such a damning crime? Why would the CIA need to protect itself from Congressional knowledge of that fact? Many Americans who knew nearly as precisely about al Qaeda's plans, and said so at the highest levels of government, are alive and well — if somewhat demoralized at having been proven so tragically prescient.

I agree with Posner's general point as cited by bamage, but the specific conclusion in the case of missing evidence doesn't add up. Means, yes. Opportunity, yes. Motive? I don't see it.