"Soon, you will know."

That is the ominous statement an uncooperative Khalid Sheikh Mohammed (KSM), mastermind of the Sept. 11, 2001, terrorist attacks, told his Central Intelligence Agency interrogators when they initially asked him, after he had been captured, about additional planned al-Qaida attacks on the United States.

In March 2003, KSM became the third and final terrorist ever waterboarded by the CIA. The other two were Abu Zubaydah and Rahim Al-Nashiri.

So few were waterboarded because the CIA was so strict in the criteria for deciding when the technique could be used.

As CIA Acting General Counsel John A. Rizzo explained in a 2004 letter to then-Acting Assistant Attorney General Daniel Levin of the Justice Department's Office of Legal Counsel, the CIA would only resort to waterboarding a top al-Qaida leader when the agency had "credible intelligence that a terrorist attack is imminent," "substantial and credible indicators that the subject has actionable intelligence that can prevent, disrupt or deny this attack" and "(o)ther interrogation methods have failed to elicit the information within the perceived time limit for preventing the attack."

Rizzo's letter, as quoted here, was cited in a May 30, 2005, memo to Rizzo from then-Principal Deputy Assistant Attorney General Steven G. Bradbury, also of the Office of Legal Counsel.

On Tuesday, the CIA confirmed to me that it stands by assertions credited to the agency in this 2005 memo that subjecting KSM to "enhanced techniques" of interrogation -- including waterboarding -- caused him to reveal information that allowed the U.S. government to stop a planned 9/11-style attack on Los Angeles.

The previously classified memo was released by President Obama last week.

Before they were waterboarded, both KSM and Abu Zubaydah did not believe Americans had the will to stop al-Qaida, the 2005 Justice Department memo says, citing information from the CIA.

"Both KSM and Zubaydah had 'expressed their belief that the general U.S. population was 'weak,' lacked resilience and would be unable to 'do what was necessary' to prevent the terrorists from succeeding in their goals,'" said the memo. "Indeed, before the CIA used enhanced techniques in its interrogation of KSM, KSM resisted giving any answers to questions about future attacks, simply noting, 'Soon, you will know.'"

After he was waterboarded, KSM provided the CIA with information that allowed the U.S. government to close down a terror cell already "tasked" with flying a jet into a building in Los Angeles.

"You have informed us that the interrogation of KSM -- once enhanced techniques were employed -- led to the discovery of a KSM plot, the 'Second Wave,' 'to use East Asian operatives to crash a hijacked airliner into' a building in Los Angeles," says the memo, referring to information CIA provided to Justice.