WASHINGTON (CNN) -- An independent commission is needed to determine who authorized the use of abusive interrogation techniques against suspected terrorists, a leading advocate of such a panel said Sunday.
Some congressional Democrats are calling for an investigation into CIA interrogation techniques.
"I want to know who was it who made the decisions that we will violate our own laws; we'll violate our own treaties; we will even violate our own Constitution," Sen. Patrick Leahy told CBS' "Face the Nation."
"That we don't know," said Leahy, D-Vermont, the chairman of the Senate Judiciary Committee. "We don't know what that chain of command was."
Former President George Bush repeatedly denied that his administration authorized the torture of prisoners in U.S. custody. But a set of legal opinions released earlier in this month documented the Bush administration's justification for coercive interrogation techniques including waterboarding, which has been considered torture since the Spanish Inquisition.
A Senate Armed Services Committee report released last week showed that top Bush administration officials gave the CIA approval to use waterboarding as early as 2002. And in 2003, a meeting that included then-Vice President Dick Cheney, CIA Director George Tenet, Attorney General John Ashcroft and National Security Adviser Condoleezza Rice reaffirmed the use of coercive tactics, according to the Senate Intelligence Committee.
The releases have fueled calls for investigations of former administration and led to arguments from Bush's defenders -- including Cheney -- that the tactics produced information that saved American lives.
Leahy first proposed the idea of a nonpartisan "commission of inquiry" in March. He said Sunday that he was not "out for some kind of vengeance," but added, "I'd like to read the page before we turn it."
"I want to know why they did that; what kind of pressures brought them to write things that are so off the wall; and to make sure it never happens again. That's why I want it."
Former Republican presidential nominee John McCain said any talk of prosecution was about "settling old political scores." McCain, who was tortured as a prisoner of war in Vietnam, fought for limits on U.S. interrogation practices during the Bush administration, but the Arizona senator said the United States needs "to put this behind us."
"We've made a commitment that we will never do this again," McCain told CBS. "No administration, I believe, would ever do this again. And it's time to fight the wars that we're in."
President Barack Obama has said his administration is not interested in prosecuting CIA officers who relied on legal advice from the administration. Obama's chief of staff, Rahm Emanuel, said last week that the administration would not pursue officials who authorized coercive interrogations, either.
But Obama appeared to back Leahy's idea last week, when he suggested that having a panel "above reproach" look into the issue would be "a more sensible approach to take." However, his spokesman, Robert Gibbs, said Sunday that a review already under way by the Senate Intelligence Committee "is the appropriate place for that."
"I think the president had great fears that the debate that you've seen happen in this town on each side of this issue, at the extremes, that's taken place, would be what would envelop any commission that looked backward," Gibbs told NBC's "Meet the Press."
The Democratic leaders of Congress have split over Leahy's "Truth Commission" proposal. House Speaker Nancy Pelosi supports it, while Senate Majority Leader Harry Reid said he prefers any inquiry be handled through the Intelligence Committee.
Sen. Dianne Feinstein, the head of the Intelligence Committee, told CNN's "State of the Union" that the committee's probe will take six to eight months.
"My hope is that the public debate quells, that we have an opportunity to do our work," said Feinstein, D-California. "The committee will consider it and then we will release, most likely, findings and recommendations."
Connecticut Independent Joseph Lieberman told CNN that an investigative commission would "poison the water here in Washington. It will achieve nothing. ... So let the Intelligence Committee do its work. That should be the end of it."
Lieberman and Sen. Lindsey Graham, R-South Carolina, criticized the release of the Bush administration memos, which came in response to a lawsuit by the American Civil Liberties Union. iReport.com: Share your take on torture
"I think it was a mistake to release the techniques that we're talking about and inform our enemy as to what may come their way," Graham said.
Graham, a lawyer in the Air Force Reserve, said the use of abusive interrogations may have produced some information, "but also to say that it's been a net positive is wrong."
"There's a way to get good information in an aggressive manner to protect this nation without having to go into the Inquisition era," he said. "I believe you can do both."
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