The CIA was under no legal obligation to videorecord its interrogation of Abu Zubaydah and Abd al-Rahim al-Nashiri, so, one might ask, why was it required to preserve the recordings it made? The answer, here as elsewhere in the law, is that the destruction of evidence is (sometimes) culpable while the non-creation of evidence is not.
Large private firms understand this point and respond in two main ways. First, most firms have routine document destruction programs. A firm that is not under active investigation for wrongdoing is not generally required to keep the "documents" (used here in the broad sense to include not only hard copies of writing but electronic files of text, audio and/or video). Indeed, the law sometimes imposes affirmative obligations on firms to destroy documents that contain sensitive personal information regarding their clients, employees and others. Even where not legally required to do so, prudent firms purge their records periodically to avoid potential legal headaches later. To repeat, this is generally lawful where there is no specific intent to frustrate a particular investigation or proceeding.
The second---and more effective---means of preventing documents from coming back to bite the firm is not to create them in the first place. Email is especially difficult to eliminate and thus can be very dangerous, which is why some sensitive issues are addressed only in unrecorded conversations.
The problem for firms is that destroying and/or not creating documents is itself costly. A well-run organization understands what it is doing, and to do so it needs to have as thorough a picture of its operations as possible. Communications by secure email and office intranets offer advantages (and corresponding disadvantages) that oral communications do not. And because it is often difficult to predict in advance just which documents will prove sensitive later on, an effective document destruction program will likely be quite over-inclusive, destroying useful as well as useless documents.
However a firm strikes the balance, it cannot, once under investigation, destroy relevant documents, and that is even more true for the government. Not only did the CIA destroy tapes it knew had been sought by others in (and outside) the government; before the destruction occurred, it apparently denied that the tapes even existed when pressed by the 9/11 Commission.
Coming so fast on the heels of the NIE reversal regarding Iran's pursuit of nuclear weapons, the news of the destruction of the Zubaydah tapes' destruction caps a very bad week for the nation's intelligence/covert ops communities, but one shouldn't immediately leap to the conclusion that an important job was (once again) bungled by the spies. Anybody paying attention knows that the failure of pre-war intelligence was essentially a case of the administration (especially VP Cheney) demanding cooked intelligence. It remains to be seen whether that was also the story of the overestimation of the nuclear threat from Iran, and it also remains to be seen how high up the responsibility for destruction of the Zubaydah tapes goes.
Posted by Mike Dorf