Why the CIA destroyed the waterboarding tapes?

Emptywheel finds a pretty big clue what CIA wanted to hide:

... the May 10, 2005 "Techniques" memo reveals that Abu Zubaydah's interrogator far exceeded OLC guidlines on how to administer waterboarding.

The IG Report noted that in some cases the waterboard was used with far greater frequency than initially indicated, see IG Report at 5, 44, 46, 103-04, and also that it was used in a different manner. See id. at 37 ("[T]he waterboard technique ... was different from the technique described in the DoJ opinion and used in the SERE training. The difference was the manner in which the detainee's breathing was obstructed. At the SERE school and in the DoJ opinion, the subject's airflow is disrupted by the firm application of a damp cloth over the air passages; the interrogator applies a small amount of water to the cloth in a controlled manner. By contrast, the Agency Interrogator ... applied large volumes of water to a cloth that covered the detainee's mouth and nose. One of the psychologists/interrogators acknowledged that the Agency's use of the technique is different from that used in SERE training because it is "for real--and is more poignant and convincing.") see also id. at 14 n14.[my emphasis]

Not only does this implicate Tenet--who was DCI at the time--for further mismanagement, but it implicates his successor Porter Goss.

Goss was in charge when the CIA - having been warned not to destroy the torture tapes - did so anyway. And this OLC memo provides proof that CIA had more to worry about than just that the identities of those depicted administering torture on the tapes would be revealed. We know that the tapes were clear evidence that the interrogators were breaking the law - exceeding even the expansive guidelines laid out in the Bybee Memo on how waterboarding should be used. This memo, in other words, proves what we already suspected - that the torture tape destruction served to obstruct justice.

As Emptywheel's linked post demonstrates, we should not be surprised that Mr. Goss is very, very upset that national security has been Teh Jeopardized!!! by the release of these memos.

... There's an even better explanation, too.