"I have been told and was assured earlier today when I called about it that when this comes out, all the details will be made available to the public, so we'll have a picture of what happened," White House spokesman Tony Snow told reporters Tuesday.

Military investigators strongly suspect that a small number of Marines snapped after one of their own was killed by a roadside bomb November 19 in Haditha, a city on the Euphrates River northwest of Baghdad, and went on a rampage, sources told CNN.

Marine Gen. Peter Pace, the chairman of the Joint Chiefs of Staff, said Monday that two investigations are being conducted -- one into the killings themselves, and the second focusing on "why didn't we know about it sooner than we knew about it."

Snow said President Bush was first briefed on the matter after a reporter for Time magazine, which first published the allegations of a massacre in March, asked the White House about it. He said Bush "is allowing the chain of command to do what it's supposed to do in the Department of Defense, which is to complete an investigation."

The Marines originally reported that 15 civilians died in a roadside bombing that also killed one Marine. A later report suggested the civilian victims may have been caught in a firefight. But senior Pentagon officials said last week that the investigation tends to support allegations that the Americans carried out an unprovoked massacre.

It was apparently the Marine's death in that roadside bombing that led to the killings.

Rep. John Murtha, D-Pennsylvania, said the allegations, if true, could do more damage to the U.S. war effort in Iraq than the 2004 revelations that American troops had tortured prisoners at Iraq's notorious Abu Ghraib prison.

"We are supposed to be fighting this war for democracy and yet, something like this happens to set us back," said Murtha, a retired Marine colonel who has become an outspoken critic of the war.

He accused commanders of trying to cover up the incident, telling CNN that U.S. military officials paid the families of those killed between $1,500 and $2,500 in the aftermath. Those payments had to be authorized at high levels, he said.

"Eighty percent of the Iraqis want us out of there, and 47 percent say it's OK to kill Americans," Murtha said. "Something like this happens, they knew about it. The Iraqis knew about it. The Americans pay them, and then it goes up the chain of command and somebody stifles it."

But Murtha praised Gen. Michael Hagee, the commandant of the Marine Corps, for going to Iraq to discuss the treatment of noncombatants with his troops.

"He is over there right now, telling the troops to protect noncombatants. The rules of engagement insist you don't fire unless you're in danger, and I understand the pressure the troops are under. That is not the point. The point is we can't let this go on."

Sources have said between four and eight Marines from Kilo company of the 3rd Battalion, 1st Marine Regiment, were directly involved in the alleged massacre. But some Marines from other units knew what happened, because they helped document the aftermath.

The sources said the investigation is likely to result in murder charges against some Marines and dereliction of duty counts against others.

The commander of the battalion involved in the incident has been relieved of his command, along with two company commanders.

Iraq's new ambassador to the United States, meanwhile, maintains that U.S. Marines "intentionally" killed his cousin last June when they were conducting a sweep in Haditha, the same volatile Anbar town where the alleged massacre occurred in November.

In an interview with CNN, Samir al-Sumaidaie said the actions were a "betrayal" of the American people and the military, and he said he is "ultimately" confident that the matter will be investigated properly.

"On the whole, the United States and the military are doing an honorable job on an honorable project, which is of immense potential benefit for the United States and for us. Such crimes detract from that."

Referring to Marines, he said that "for every bad apple," there are "thousands and thousands" trying to do a job under tough conditions. (Full story)

Speaking in London, Iraqi Prime Minister Nouri al-Maliki said the killings of civilians in Haditha were not justified and cautioned that coalition troops need to show more care, The Associated Press reported

"We emphasize that our forces, that multinational forces, will respect human rights, the rights of the Iraqi citizen," al-Maliki said through an interpreter, according to the AP. "It is not justifiable that a family is killed because someone is fighting terrorists. We have to be more specific and more careful."