The senior Pentagon official in the Bush administration’s system for prosecuting detainees said in a published interview that she had concluded that interrogators had tortured a Guantánamo detainee who has sometimes been described as “the 20th hijacker” in the 2001 terrorist attacks.

The public record of the Guantánamo interrogation of the detainee, Mohammed al-Qahtani, has long included what officials labeled abusive techniques, including exposure to extreme temperatures and isolation, but the Pentagon has resisted acknowledging that his treatment rose to the level of torture.

But the official, Susan J. Crawford, told Bob Woodward of The Washington Post that she had concluded that his treatment amounted to torture when she reviewed military charges against him last year. In May she decided that the case could not be referred for trial but provided no explanation at the time.

“His treatment met the legal definition of torture. And that’s why I did not refer the case” for prosecution, Ms. Crawford was quoted as saying in an article published in The Post on Wednesday.