Al Maumausolo surveys what is left of the windswept, hilltop battlefield he has not seen in 42 years and says: "The body's somewhere around here."

Sergeant David White checks his notes on Hill 881 in Vietnam during a search to find the remains of a US soldier

US soldiers carry a coffin containing what may be the remains of a US serviceman killed during the Vietnam War

Vietnam War veteran Al Maumausolo (front) hikes up Hill 881 South in Quang Tri province

The US Marine Corps veteran has returned to this mountain near the key Vietnam War battle site of Khe Sanh to help a group of United States military investigators pinpoint the site where remains of a Marine could be found.

Since the end of US combat involvement in 1973, 655 Americans listed as missing during the war have been repatriated from Vietnam and identified but 1,313 remain unaccounted for, the US says.

It is the job of the Hawaii-based Joint POW/MIA Accounting Command (JPAC) to investigate those missing-in-action cases, and to recover the remains of those they find.

One of those cases has brought an investigation team to this mountain they call Hill 881 South, in central Vietnam's Quang Tri province.

With a clear view for kilometres (miles) around, Hill 881 South offered the perfect spot for Maumausolo's six-man reconnaissance team to conduct observations and set up a radio relay point.

They dropped in by helicopter one day in August 1968. Maumausolo rappelled down, and landed right on the smelly corpse of an American soldier.

"I fell on my butt... I got up and I'm looking right at it," recalls Maumausolo, 63.

After recovering from his initial shock, Maumausolo pushed the body into a foxhole and buried it as well as he could.

The abandoned foxholes are shallow depressions in the ground, now overgrown with tall grass.

Vietnamese workers chop away the vegetation to let an explosive ordnance disposal (EOD) technician sweep the holes with a metal detector. It whines like a baby, signalling dirt-encrusted pieces of barbed wire and other war debris but nothing that confirms precisely where the missing marine's remains lie.

"You don't think you were down any more this way?" asks David White, the US Army sergeant leading this investigation.

No, replies Maumausolo. "This is the right area."

He moves to another foxhole and says, "Try this one." White helps to hack away the grass.

At 48, White is a six-year member of the investigation team. He speaks Vietnamese and has a gentle manner that belies the battle-hardened look of his face.

The job, he says, is "a great honour."

Like other members of the team, White dresses in casual clothes and carries no weapon.

He says his work could be compared with that of a police detective, looking for evidence and witnesses.

Among the documents White brings to the site is a black-and-white picture of the missing marine.

Explosions once shook this now-quiet hill which is still littered with discarded ammunition, the remains of missiles, and other ordnance.

Along with the EOD technician, White's team includes a photographer, an Army Special Forces medic, and Chuong Vu, 33, a US Air Force member who has spent almost six years with the unit.

"I really love what I'm doing," says Vu, who was born in Vietnam but immigrated to the US in 1991. He serves as a linguist and analyst.

"Everything I'm doing is for the country, for America," Vu says.

The Americans work alongside Vietnam's Office for Seeking Missing Persons (VNOSMP), a liaison team. Days before White's group arrives, VNOSMP officers have checked how to reach the site, and have lined up a local witness, Le Huu Hanh, 64. He served with a North Vietnamese regiment at Hill 881 South in July 1968.

White politely interviews him in a hotel lobby the night before they visit the hill.

Hanh recounts how his unit shot an American and then tried to use his body as "bait" to lure other US soldiers. After three days the smell forced them to bury the body in an unmarked site next to a crater.

"Can you describe the body?" White asks.

"Full uniform on with boots and everything... about 18 years old," says Hanh.

White asks for more details on the burial location, which Hanh says was on flat ground just a few metres (yards) from a stream.

Hanoi says about 300,000 North Vietnamese soldiers are also still listed as missing from the war.

But Hanh, a farmer, tells AFP that times have changed and as a fellow soldier he wants to help the Americans find their comrade.

"Now the Americans and Vietnamese work together," he says.

White tells AFP that Hanh's information matches what investigators know of the incident. It also seems to fit with what Maumausolo found on the hill about five weeks after Hanh was there.

But when Hanh, Maumausolo and the investigators reach the mountain next morning after a bumpy drive and a short hike, they discover the two sites do not match.

Hanh's site, dotted with short pine trees near a bomb crater, is about 60 metres downhill from the foxholes that Maumausolo found.

Even with the "puzzling" apparent movement of the body, White believes there is enough evidence to recommend an excavation.

"Our job's not to try to dig up remains. We just find it, get enough evidence to say we believe he was here," White says.

His report to officials in Hawaii will recommend that a separate group of JPAC specialists, known as the recovery team, dig up the area indicated by Maumausolo, with Hanh's site as a secondary excavation if needed.

He and other JPAC members say they are fulfilling a pledge made to all US military personnel: that they will not be forgotten.

Maumausolo said he hopes the effort will help bring peace of mind not only to the missing soldier's family, but to his friends -- and to himself.

"Sometimes I get nightmares bad, about this case," he said. "A lot of his friends gave me their numbers. 'If you find anything, call us', they said."