A Pentagon official acknowledged in an interview published Wednesday that the United States tortured Mohammed al-Qahtani, a Saudi man who allegedly had hoped to become the "20th hijacker" in the Sept. 11 attacks.

"We tortured Qahtani," said Susan J. Crawford, a retired judge who was appointed convening authority of military commissions in February 2007. Crawford was interviewed by The Washington Post's Bob Woodward.

Al-Qahtani was one of six men charged by the military in February 2008 with murder and war crimes for their alleged roles in the 2001 attacks. But in May, Crawford decided to dismiss the charges against al-Qahtani, who was being held at the U.S. military prison at Guantanamo Bay, Cuba.

His Pentagon-appointed lawyer, Army Lt. Col. Bryan Broyles, suggested at the time that his client's harsh interrogation, authorized by then defence secretary Donald Rumsfeld, could have influenced the decision.

"In any instance in which the United States wishes to impose the death penalty, my opinion is that such a case requires clean hands on the part of the U.S.," Broyles told The Associated Press in May.

Al-Qahtani in October 2006 recanted a confession he said he made after he was tortured and humiliated at Guantanamo.

The alleged torture, which he detailed in a written statement, included being beaten, restrained for long periods in uncomfortable positions, threatened with dogs, exposed to loud music and freezing temperatures and stripped nude in front of female personnel.

In the interview published by the Post on Wednesday, Crawford said: "His treatment met the legal definition of torture. And that is why I did not refer the case" for prosecution.