Two US Marines ordered to photograph the corpses of more than 20 unarmed Iraqi civilians allegedly massacred by their comrades were left severely traumatised by the sight, according to the soldiers' parents.

Lance Corporal Andrew Wright, 20, and Lance Corporal Roel Ryan Briones, 21, both Marines based at Camp Pendleton, California, were sent to photograph and remove the bodies of up to 24 Iraqi men, women and children who were shot last November in the western Iraqi city of Haditha.

According to their parents, both men have struggled with post-traumatic stress disorder ever since. What they saw that day has become the subject of two US military investigations and is threatening to become, alongside Abu Ghraib, a defining horror of the American-led invasion of Iraq.

Iraqi witnesses and US politicians who have seen evidence from the investigations say that a group of Marines from Kilo Company, 3rd Battalion, 1st Marine Regiment, 1st Marine Division, went on the rampage after a popular soldier was killed by a roadside bomb.

US soldiers allegedly shot up a taxi before going from house to house, throwing grenades and killing a family at close range.

Several members of Kilo Company are currently confined to their barracks in Camp Pendleton, between San Diego and Los Angeles, while the investigations, one focusing on the alleged killings, the other on an alleged military cover-up, reach their conclusion.

As Americans spent Memorial Day weekend digesting news reports from Haditha, including a Times investigation into the alleged killings, General Peter Pace, the chairman of the Joint Chiefs of Staff, and the most senior uniformed US officer, urged the country not to jump to conclusions about what took place.

"We want to find out what happened and we'll make it public," he told CNN. "If the allegations, as they are being portrayed in the newspaper, turn out to be valid, then of course there will be charges. But we don't know yet what the outcome will be."

The mother of Corporal Briones said her son was ordered to take pictures of the bodies in Haditha on his personal digital camera, which he was then told to hand over to the US Navy. "It was horrific. It was a terrible scene," she told the Associated Press.

Mrs Briones called the incident "a massacre" and said Corporal Briones, who won a Purple Heart after he was injured on his first tour of duty in Iraq, had found himself moving the body of a young girl who had been shot in the head. "He had to carry that little girl’s body," she said, "and her head was blown off and her brain splattered on his boots".

Corporal Wright’s parents, Patty and Frederick Wright of Novato, California, declined to say what might have happened to the pictures their son took, but said he had turned over all of his information to the Navy. "He is the Forrest Gump of the military," Mr Wright said. "He ended up in the spotlight through no fault of his own."

The spark to the violence was the death of Lance Corporal Miguel Terrazas, 20, of El Paso, Texas, a close friend of Corporal Briones, who was killed by a roadside bomb as his patrol passed through the streets of Haditha, a notorious base for insurgents.

Interviewed yesterday on National Public Radio, Corporal Terrazas's uncle, Andy Terrazas, a former Marine, said: "I hope this is over soon so they can just let him rest in peace. I hope these Marines come out clean, but I guess it's not looking too good, right?"

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