The Al-Qaeda mastermind of the September 11 attacks mocked his CIA interrogators during waterboarding sessions by counting how long it would last.

Marc Thiessen, a former aide to President George W. Bush, discussed the interrogations of Khalid Sheikh Mohammed during a panel appearance at the American Enterprise Institute in Washington Monday. Thiessen first reported the lengths KSM went to in his best-selling book, "Courting Disaster: How the CIA Kept America Safe & How Barack Obama is Inviting the Next Attack," released last year. Thiessen said that KSM, with his arms restrained, would use his fingers to count off the seconds during each waterboarding session, until the legal guidance of 40 seconds was reached.

Writing on Tuesday's Enterprise Blog, Thiessen recalled an excerpt in his book that he says proved KSM was determined not to cooperate with his interrogators. "Those familiar with the CIA's interrogations say there is no way we could have gotten KSM to talk without waterboarding... A high-ranking CIA official told me, ‘Everyone will tell you, even people opposed to the program, that [KSM] was not going to talk otherwise. I mean, this was one tough mother. He would get waterboarded and they would watch his fingers because he'd figured out how long it was going to last, and he'd just count on his hands how long he had to hold out.'"

During the panel discussion Thiessen attempted to make the point that interrogations of high value prisoners could be compromised if they understood the tactics. In regard to getting good and credible information from KSM and other enemy combatants Thiessen said, "The key to the success of breaking these people is that they can't know what they're facing. And if they do know, they can resist it."

Since the killing of the world's most wanted terrorist, Usama bin Laden, two weeks ago, there has been much debate about the interrogation methods used during the Bush administration. Many people are now arguing that those same harsh tactics are what ultimately provided the intel to find bin Laden.

Thiessen criticizes President Obama for scaling back on less confrontational techniques of interrogation, early on in his presidency. But Obama's national security adviser at the time, Gen. James Jones, argued the president's decision in 2009 was correct. Jones was at a separate luncheon in Washington Monday, and said, "This debate will continue and we'll see where it goes."

Kelly Wright is a general assignment reporter for Fox News Channel (FNC), based in the Washington, D.C. bureau. He is also a co-host on "America's News Headquarters" on Saturdays (1:00-2:00 PM/ET). Wright previously served as a co-host on "Fox & Friends Weekend." Click here for more information on Kelly Wright