An administration that defends waterboarding isn't capable of conducting an honest investigation into why the CIA destroyed videotapes of the torture sessions.

The Justice Department and the CIA started preliminary inquiries Saturday, but Sen. Joseph R. Biden Jr. (D., Del.) is right: A special counsel is needed to investigate this potential obstruction of justice. The Bush administration is only too relieved those tapes won't be showing up on YouTube.

Attorney General Michael B. Mukasey arrived after waterboarding was discontinued. But he, too, has shown a lack of moral fortitude on the subject.

During his confirmation hearing, Mukasey couldn't decide whether it was torture to strap a detainee to a see-saw, tilt him head-down and pour water into his mouth and nose to simulate drowning. Maybe seeing the videotapes would have helped him decide. Given that, how can Mukasey be expected to lead a fair and independent probe into the destruction of the torture tapes that depicted this shameful technique?

Under current law, of course, Mukasey would need to approve the appointment of a special counsel. But that would at least be better than keeping the probe under the direction of the

ambivalent general

, whose boss, President Bush, still defends torturing terrorism suspects, but also says the United States doesn't torture people. Go figure.

The CIA's explanations for destroying the tapes don't wash. CIA Director Michael V. Hayden said the tapes, made in 2002, were destroyed in 2005 to protect the identities of the interrogators. (Guess those rules didn't apply to CIA agent Valerie Plame.)

With all the technological expertise at its disposal, couldn't the CIA find a way to blot out the identities of its agents on tape? Hayden's explanation implies the CIA has no other documents in its vaults that could reveal an operative's name.

The more likely explanation is that officials realized these tapes implicated CIA operatives in a felony called torture. That's probably why the agency didn't turn over the tapes, as it should have, to the Sept. 11 commission in 2004. It's no coincidence that the tapes were destroyed in the midst of heightened scrutiny over the CIA's secret detention program.

Bush has defended waterboarding, saying it and other "harsh" methods have yielded crucial intelligence. But waterboarding is no longer included in a classified executive order spelling out approved interrogation techniques for detainees.

In the long debate over torture, the disappearance of these tapes is the strongest indication yet that the Bush administration knew its approved interrogation methods were illegal. Officials could draw up secretly legal justifications for these tactics, but they knew the court of public opinion and international law would never sanction them.