In the Marine Corps, they are quietly calling it their My Lai, the massacre of hundreds of villagers in 1968 that became a symbol for American brutality in the Vietnam war. In this generation's war, the village is Haditha, north-west of Baghdad, where US marines killed two dozen Iraqi civilians, including 11 women and children.
In what is being viewed as the gravest allegation to date of war crimes in Iraq, a military investigation is expected to present findings in Baghdad next week that a small group of troops shot dead 24 unarmed Iraqi civilians, including five men in a taxi, and women and children at homes in the town last November 19.
Other marines then tried to cover up the killings, the investigation has found.
Two lawyers quoted yesterday by the New York Times said they thought the investigation could result in murder charges, making the events at Haditha the worst case of abuse in three years of war.
The Los Angeles Times said the report would conclude that a dozen marines acted improperly and could face charges including murder, negligent homicide, dereliction of duty, and falsifying reports.
Allegations of a massacre at Haditha, a largely Sunni town active in the insurgency, were first reported by Time magazine last March. But the full scale of what happened has been slow to emerge.
"This is not a grey area. It is not a combat situation confused by the fog of war. This was a massacre," said John Sifton of Human Rights Watch. "If these allegations are borne out, and it looks like they will be, this will be the most serious war crime that has taken place in Iraq."
Military officials in Baghdad initially claimed that the Iraqi civilians killed last November 19 were the victims of a roadside bomb, which exploded near a bus and a military Humvee, killing one marine and 15 Iraqis. Later, officials said the civilians were killed in rapid exchanges of fire between marines and Iraqi militants who had opened fire on the convoy.
However, evidence later gathered by the Naval Criminal Investigative Service suggested that the bloodshed took place over three to five hours.
Yesterday, the LA Times quoted a senior defence department official as saying that none of the 24 Iraqis was killed by the bomb. Although Haditha has proved one of the deadliest cities in Iraq for US troops, none of the marines had come under serious hostile fire on that day.
Officials said most of the bullets were fired from a small number of rifles, although as many as a dozen members of the marine unit are under investigation.
With the investigation approaching completion the Pentagon has begun to try to avoid outrage in Congress as happened two years ago when abuse at Abu Ghraib prison first became public knowledge.
Members of Congress briefed by the Marine Corps have been horrified. Last week, John Murtha, a former marine and Vietnam veteran and a Democratic Congressman who opposes the war, issued a statement saying the civilians had been killed in cold blood by marines who had snapped under the pressures of war.
The episode has also led to serious concern within the Marine Corps about an erosion of values and morale in the midst of a long and brutal insurgency. On Tuesday, the top marine commandant, General Michael Hagee, left for Iraq to deliver speeches on "the American way of war".
However, human rights officials and some members of Congress say they are deeply troubled by the Marine Corps' response to the Haditha killings.
The killings at Haditha mark at least the third time US military officials have presented shifting official versions of events in Iraq, a record that, critics say, has damaged the Pentagon's credibility. Over the last year, the Pentagon has been embarrassed by its campaign to concoct a hero's death in Afghanistan for the football star Pat Tillman, although he was in fact killed by his fellow US Rangers in friendly fire.
The Pentagon also fabricated tales about a wounded and captured private, Jessica Lynch, that were later debunked.
"The real issue now is to move forward in the investigation in a way that fosters public confidence instead of having a plethora of investigations that are so numerous and diffuse that we don't know where they are going," said Eugene Fidell, a military lawyer in Washington.
'Then they killed my granny' - One girl's story
Time magazine, which broke the story about Haditha in March, interviewed Eman Waleed, 9, who lived near to the site of the roadside bomb which killed a marine. She said: "We heard a big noise that woke us all up. Then we did what we always do when there's an explosion: my father goes into his room with the Qur'an and prays that the family will be spared any harm."
She said the rest of the family gathered in the living room. Eman says she "heard a lot of shooting, so none of us went outside. Besides, it was very early, and we were all wearing our nightclothes." When the marines entered the house, they were shouting in English. "First, they went into my father's room, where he was reading the Qur'an," she claims, "and we heard shots."
According to Eman, the marines then entered the living room. "I couldn't see their faces very well - only their guns sticking into the doorway. I watched them shoot my grandfather, first in the chest and then in the head. Then they killed my granny."
She claims the troops started firing toward the corner of the room where she and her younger brother, Abdul Rahman, 8, were hiding; the other adults shielded the children from the bullets but died in the process. Eman says her leg was hit by a piece of metal and Abdul Rahman was shot near his shoulder.
"We were lying there, bleeding, and it hurt so much. Afterward, some Iraqi soldiers came. They carried us in their arms. I was crying, shouting, 'Why did you do this to our family?' And one Iraqi soldier tells me, 'We didn't do it. The Americans did.'"