From an Op-Ed piece by Ali Soufan, a former FBI special agent, in the New York Times:

[…]

It is inaccurate, however, to say that Abu Zubaydah had been uncooperative. Along with another F.B.I. agent, and with several C.I.A. officers present, I questioned him from March to June 2002, before the harsh techniques were introduced later in August. Under traditional interrogation methods, he provided us with important actionable intelligence.

We discovered, for example, that Khalid Shaikh Mohammed was the mastermind of the 9/11 attacks. Abu Zubaydah also told us about Jose Padilla, the so-called dirty bomber. This experience fit what I had found throughout my counterterrorism career: traditional interrogation techniques are successful in identifying operatives, uncovering plots and saving lives.

There was no actionable intelligence gained from using enhanced interrogation techniques on Abu Zubaydah that wasn’t, or couldn’t have been, gained from regular tactics.

[…]

[From Op-Ed Contributor – My Tortured Decision – NYTimes.com]