Notes from a series of meetings at the Pentagon in early 2003 -- obtained by ABC News -- show that Alberto Mora, general counsel of the Navy, warned his superiors that they might be breaking the law.

During a January 2003 meeting involving top Pentagon lawyer William Haynes and other officials, the memo shows that Mora warned that "use of coercive techniques ... has military, legal, and political implication ... has international implication ... and exposes us to liability and criminal prosecution."

Mora's deep concerns about interrogations at Guantanamo have been known, but not his warning that top officials could go to prison.

In another meeting held March 8, 2003, the group of top Pentagon lawyers concluded -- according to the memo -- "we need a presidential letter approving the use of the controversial interrogation to cover those who may be called upon to use them."

No such letter was issued.

White House: Tactics Are Legal

Today, the White House insisted that tactics used at Guantanamo Bay are now -- and have been -- legal.

"All interrogation techniques that have been approved are lawful and consistent with our obligations," said White House press secretary Scott McClellan.

In another internal memo obtained by ABC News, a Navy psychologist observing the interrogation warned that the tactics used against Mohammed al Qahtani -- dubbed "the 20th hijacker" -- revealed "a tendency to become increasingly more aggressive without having a definite boundary."

Secretary of Defense Donald Rumsfeld said Tuesday that interrogating al Qahtani had produced results.

"Qahtani and other detainees have provided valuable information, including insights into al Qaeda planning for September 11th, including recruiting and logistics," he said during a news conference.

Human rights lawyers say Mora was right to raise objections to what his superiors were doing.

"It's clear that individuals who engage in abusive treatment of this nature may be criminally liable for the conduct that they engage in," said Deborah Pearlstein, the director of the U.S. Law and Security Program at Human Rights First. "So if I were one of the troops who was being asked to conduct interrogations using these techniques, I would certainly want to ask my lawyer whether he thought this was legal."