A week ago, John Warner, chairman of the Senate Armed Services Committee, said he was satisfied that Defense Secretary Donald Rumsfeld was keeping his promise to leave no stone unturned to investigate the atrocities of Abu Ghraib prison. A newly released report by the Army's inspector general shows that Mr. Rumsfeld's team may be turning over stones, but it's not looking under them.

The authors of this 300-page whitewash say they found no "systemic" problem - even though there were 94 documented cases of prisoner abuse, including some 40 deaths, 20 of them homicides; even though only four prisons of the 16 they visited had copies of the Geneva Conventions; even though Abu Ghraib was a cesspool with one shower for every 50 inmates; even though the military police were improperly involved in interrogations; even though young people plucked from civilian life were sent to guard prisoners - 50,000 of them in all - with no training.

Never mind any of that. The report pins most of the blame on those depressingly familiar culprits, a few soldiers who behaved badly. It does grudgingly concede that "in some cases, abuse was accompanied by leadership failure at the tactical level," but the report absolves anyone of rank, in keeping with the investigation's spirit. The inspector general's staff did not dig into the abuse cases, but merely listed them. It based its findings on the comical observation that "commanders, leaders and soldiers treated detainees humanely" while investigators from the Pentagon were watching. And it made no attempt to find out who had authorized threatening prisoners with dogs and sexually humiliating hooded men, to name two American practices the Red Cross found to be common. The inspector general's see-no-evil team simply said it couldn't find those "approach techniques" in the Army field manual.

Even the report's release on Thursday was an exercise in misdirection, timed to be overshadowed by the 9/11 commission's report. Senators on the armed services panel were outraged at the report's shoddiness and timing, but should not have been surprised. The Defense Department has consistently tried to stymie Mr. Warner's investigation. It "misplaced" thousands of pages from Maj. Gen. Antonio Taguba's report on Abu Ghraib, the only credible military account so far. It stalled the completion of a pivotal look at Army intelligence by two other Army generals until lawmakers went off to the political conventions and summer vacations. And it ignored Senate demands for the Red Cross reports on American military prisons for months.

The Pentagon finally brought those documents to the Senate in the last two weeks, in a way that ensured they would be of minimal use. The voluminous reports were shown briefly to senators and a few members of the Armed Services Committee staff after the senators' personal aides were ushered out. Then the reports were hauled back to the Pentagon.

Mr. Warner has admirably resisted pressure from the White House and Republican leaders in Congress to stop his investigation. But he is showing signs of losing appetite for the fight. Mr. Warner held only one hearing in the last month - on the new report - and agreed to the ground rules on the Red Cross reports. We've always been skeptical that the Defense Department can investigate itself credibly, and now it's obvious that it plans to stick to the "few bad apples" excuse. The only way to learn why innocent Iraqis were tortured by American soldiers is a formal Congressional inquiry, with subpoena power.