Washington ? An Army general who investigated Iraqi prison abuse differed sharply Tuesday with a top Pentagon civilian leader over who was in charge of the Abu Ghraib prison in Iraq when the humiliation and sexual abuse of prisoners took place last year.

More than five months after the abuses first were reported, the two men — Maj. Gen. Antonio Taguba and Stephen Cambone, undersecretary for intelligence — still differed on who ultimately was responsible for actions inside the prison.

The pair also differed on whether military interrogators had overstepped their authority by enlisting the help of guards in “setting the conditions” for fruitful interrogations. Military police later created the scenes of humiliation and sexual abuse shown in pictures that have shocked the world.

Taguba at one point said he found no policy that authorized or condoned those abuses at Abu Ghraib prison. He attributed them largely to military, CIA and civilian interrogators who convinced military police guards to assist them by abusing prisoners under their control. But, he said, the MPs “acted on their own volition.”

Senators from both parties, however, questioned whether that truly was the case.

“The collars used on prisoners, the dogs and the cameras did not suddenly appear out of thin air. These acts of abuse … were clearly planned and suggested by others,” said Sen. Carl Levin of Michigan, ranking Democrat on the Senate Armed Services Committee.

At a second hearing in the afternoon, the Army’s intelligence chief told the committee that military interrogators could have used a variety of techniques on Iraqi prisoners, including sensory deprivation, solitary confinement for more than 30 days, sleep-pattern alterations and the use of uncomfortable “stress positions” for at least 45 minutes at a time.

But Lt. Gen. Keith Alexander told the Senate panel that interrogators did not request the use of the additional procedures even though interrogators were under extreme pressure to find out who was behind an anti-U.S. insurgency.

Alexander said the added procedures were within the Geneva Convention guidelines but must be used sparingly, and only with the approval of a ranking general.

Among the procedures approved for all prisoners were giving incentives for good behavior, convincing prisoners that interrogators already know everything or that resistance is futile, rapid fire questioning, or silence.

The hearings Tuesday came as the Pentagon continued to weigh whether to release photographs to the public. They reached an agreement Tuesday night to release images to Congress today behind closed doors.

The hearings, however, underscored just how difficult it will be for the Pentagon to determine who was responsible for the abuses.

Taguba said he found dramatic lapses in command responsibility up to the prison system commander, Brig. Gen. Janis Karpinski but acknowledged his review stopped there and that he didn’t examine what higher-ups in Iraq or at the Pentagon knew or authorized.

Committee chairman Sen. John Warner, R-Va., asked Taguba: “In simple words, your own soldier’s language, how did this happen?”

“Failure in leadership, sir, from the brigade commander on down,” came the crisp response from the two-star general, a previously little-known 32-year Army veteran whose father was held prisoner by the Japanese in World War II. “Lack of discipline, no training whatsoever, and no supervision.”

But even as he sat elbow-to-elbow with Cambone at the witness table, Taguba said he felt it was clear that a military intelligence brigade effectively had been given custody of the prison by a November 2003 order from Lt. Gen. Ricardo Sanchez. Cambone insisted that Taguba was incorrect, and that responsibility for handling the detainees had remained with military police originally put in charge.

In addition, Cambone told the committee that he supported a recommendation from the head of Guantanamo Bay military prison that military police guards should be “collaborating” with interrogators to get useful information. Taguba disagreed, saying there should be a firewall between guards and interrogators.

That gets to a key controversy in the abuse scandal — over the role of the new head of Abu Ghraib, Maj. Gen. Geoffrey Miller, who formerly ran Guantanamo Bay. Miller visited Iraq in September, the month before the abuses occurred, and encouraged a policy of having military police “set the conditions” for interrogations.