02/08/2011 09:32 am ET Updated May 25, 2011

Donald Rumsfeld: Harsh Interrogation Helped 'In Saving Lives,' 'Troubled' Me

Former Secretary of Defense Donald Rumsfeld reportedly believes that harsh interrogation tactics used during his overseeing of the Bush administration's "War on Terror" had helped "in saving lives," but that the severity of techniques had occasionally left him "surprised and troubled."

According to ABC News, which has released a preview of Rumsfeld's interview with Diane Sawyer, the former defense secretary claimed that the interrogation of 9/11 plotter Mohammad al-Qahtani provided valuable information that saved American lives.

"Qahtani, who was the 20th hijacker, they say -- he gave a lot of information," Rumsfeld said. "And it was very helpful to our interrogators and to the United States government in saving lives."

Rumsfeld later concluded that "the fact that we haven't had an attack in a decade is a credit to that administration, the Bush administration, and to [President Bush]."

Yet in his memoir, Known & Unknown, which is set for release Tuesday, Rumsfeld claims that he was "surprised and troubled" by some of the most extreme techniques used on Qahtani, actions that he says were not even authorized.

Of the most controversial, ABC reports:

Qahtani would be subjected to sexual humiliation and long periods of sleep deprivation and isolation while in custody at Guantanamo, and his heartbeat at one point dropped to 35 beats per minute.

"I didn't approve any of that," Rumsfeld told ABC News in their interview. "And when I found out that they had done some of those things, the people who had done things that had not been approved were dealt with. They were stopped and prosecuted."

Rumsfeld continued, telling Sawyer that he had intended for all detainees to be "treated humanely."

For more on the interview, click over to ABC News.