It was the tragic final act of US military operations in Indochina in the 1970s, coming only 12 days after the chaotic rooftop evacuation of the US embassy in Saigon.

The botched rescue attempt of the crew of US container ship Mayaguez from Koh Tang, 43 kilometres off the coast of Sihanoukville, left 41 US marines and airmen and numerous Khmer Rouge fighters dead.

Since the 1990s, ongoing efforts to recover the remains of those killed in the assault on Koh Tang and Sihanoukville – including three marines who are thought to have been left behind, tortured and executed by the Khmer Rouge – have thus far failed to identify the missing.

An internal memo released last week by the Stars and Stripes newspaper suggests efforts to identify the mortal remains of several marines and airmen have been plagued by “a pattern of malfeasance of duty and abuse of scientific ethics”.

The 2011 memo, from forensic anthropologist Jay Silverstein to the then-Joint POW/MIA Accounting Command (JPAC) chief Army Major General Stephen Tom, points to “a clear violation of standard procedures” and “a failure to meet the standards and responsibilities” for “the accounting of missing Americans”.

The memo describes how investigators left no written records of their excavations.

“Such voids in our record seriously hamper current and future efforts at recovery and have and will result in the outlay of resources to redo and record work that had already been done,” Silverstein wrote.

The “failure to fully record work executed”, he went on, “may cover the only evidence thus far related to the possible fate of one of those that was left behind”.

The US embassy yesterday referred questions to JPAC, which had not responded to requests for comment at the time of going to press. Silverstein could not be reached.

In December 2010, the Ministry of Commerce issued a 99-year lease to Monarch Investment – a consortium of Russian investors – to turn Koh Tang into a $1 billion tourist resort, complete with five-star hotels, a church and a dock to accommodate cruise ships.

The development could complicate future attempts to carry out further excavations.

Brigadier General Kheng Tito, spokesman for the military police, was with JPAC officials on their first mission to Koh Tang in 1998.

“In 1998, I joined this team to research US missing in action at Koh Tang,” he said. “Now, I don’t know [what will happen], but if any firm does this business at Koh Tang, maybe [it will] jeopardise [future excavations].”

A representative of Monarch Investment declined to comment on the ongoing development of the island and efforts to recover the fallen soldiers, adding that the company’s directors were on a business trip in Russia.

In 2000, a former Khmer Rouge platoon commander on Koh Tang told the Post: “If we’d known the Americans would have come back some day to look for the bodies, we would have put all the bodies in one easy-to-find place.”