Sean Flynn could have done anything he wanted. For a while he tried to be an actor like his swashbuckling father, Errol. But the passion that drove him was to work as a photographer covering America's deadly wars in Indochina.

The dangerous, chaotic assignment brought him excitement and fame, but it also led him to his death. Forty years ago next week, Flynn and another journalist, Dana Stone, disappeared without trace after encountering a hostile checkpoint south-east of Phnom Penh.

Now, forensic tests are to be performed on remains that have been dug up in rural Cambodia by two amateur "bone hunters" who claim they have finally answered the mystery as to what happened to the two men, among three dozen journalists to have lost their lives during the war in Cambodia. John Johnson, a spokesman for the US embassy in Phnom Penh, said the remains had been sent to the Pentagon's Joint POW/MIA Accounting Command (JPAC) located in Hawaii where the tests will be conducted.

"Last Friday, the possible remains were delivered to us and we have taken action," he said. "It is hard to speculate how long the tests will take. All these cases are individual."

Yet the possible discovery of the remains of Flynn, who was aged 28 when he disappeared, has sparked controversy. Not only are the two men who made the find seeking to sell their story to the highest bidder, but a former colleague of the journalists believes the excavation of the burial site was conducted unprofessionally and may have disturbed a larger grave in which the remains of other journalists may lie.

The remains handed over to the US authorities in Cambodia were found by Briton Keith Rotheram and Scottish-born Australian David MacMillan more than two weeks ago. Reports say they were alerted to the location in Kampong Cham province in eastern Cambodia by a local man who claimed to have been a witness to the execution of a tall, blond foreigner. The witness claimed the foreigner had been forced to dig his own grave before he was battered to death.

The two men hired bomb disposal experts, a bulldozer and teams of local people to excavate the site in the village of Phka Dong, where they uncovered clothes, bone fragments and teeth. Contacted yesterday by The Independent, Mr Rotheram, who runs a guesthouse in the town of Sihanoukville, refused to answer any questions about the discovery, the full story of which, he said, would "be for the highest bidder".

Mr MacMillan claimed elsewhere that the four-month search had been partly funded by Flynn's half-sister. Yet the excavation of the site has been criticised by a colleague of the journalists who has led the search for them almost ever since they went missing. Tim Page, a British photographer celebrated for his work in Vietnam and other conflicts, said he believed a number of other foreign journalists may have been executed and buried at the same site.

Mr Page, 64, who is featured in Michael Herr's classic memoir of the Vietnam war, Dispatches, said he had led an excavation of the same site last year and found glass vials, bone fragments and teeth that he had handed to JPAC, along with GPS co-ordinates. He said it was vital a thorough examination of the site be conducted as local people claimed it held the remains of more than one foreigner killed by the Khmer Rouge.

"I have had hundreds of people contact me over the years about Sean and I'm always interested in what they have to say," Mr Page, who now lives in Brisbane, told The Australian. "But there is a very strict procedure to be followed when digging at a site of possible human remains, and in this case that has not been followed... It was not a forensic dig. They used an excavator and uncovered a full set of remains, which they removed from the site."

Sean Flynn was the child of the famed leading man and his first wife, Lili Damita, a French actress who spent huge sums of money to search for her son after he disappeared. Eventually, the photojournalist was declared officially dead in 1984, more than a dozen years after he was seized at a checkpoint and handed over to Khmer Rouge rebels. His mother died in 1994.

The 1970-75 conflict in Cambodia, a spillover of America's war against the North Vietnamese, pitched the US-backed government headed by Lon Nol against Khmer Rouge insurgents supported by the government in Hanoi. The war was eventually won by the Maoist-influenced Khmer Rouge forces, which then put in place a murderous four-year regime that caused the death of up to 2 million people.

Flynn and Stone went missing on 6 April 1970, the former on assignment for Time magazine and his colleague for CBS News. The two men were part of a larger group of journalists who had driven out of Phnom Penh on Highway One, heading toward the Vietnamese city then called Saigon, for a press conference organised by the government. One of the last Westerners to see the men was Stephen Bell, a reporter with ABC News, who would later go on to anchor Good Morning America. Speaking last night from Indiana, Mr Bell, who is now retired, said most of the reporters had travelled in large limousines, previously used by tourists but later taken over by the press corps. However, Flynn and Stone had been travelling by themselves on motorcycles.