Mr. Cheney claims that the waterboarding saved thousands of lives. Most accounts that don’t come from officials involved in the formation of those policies suggest that that is not the case. The question needs to be answered so Americans can decide if they want to buy into Mr. Cheney’s view that the ends always justify such barbaric means.

Americans also need to know who pushed the Justice Department lawyers to twist the law and the Constitution to excuse torture. And we need to know the legal reasoning, if any, behind former President George W. Bush’s decision to authorize illegal tapping of Americans’ telephones and e-mail accounts.

We need to know the legal reasoning, planning and authorization behind Mr. Bush’s program of “extraordinary rendition”  in which people were abducted and sent to countries where it was obvious to all that they were in danger of being tortured, or would be tortured.

Until these questions are answered, there is no way to ensure that these abuses will never be repeated. And the only way to get those answers is with a full investigation that has both stature and subpoena power.

The report on detainee abuse in Iraq, released by the Senate Armed Services Committee this week, showed how decisions made at the White House on detainee abuse led directly to Abu Ghraib. Among the documents that still need to be released is a Justice Department report on the attorneys who wrote the torture apologias. It was finished last year, but it was bottled up by then-Attorney General Michael Mukasey, who wanted to give those very lawyers a chance to read and amend it. The C.I.A. should also declassify its inspector general’s report on detainee abuse.