MORE THAN 1.5 million people died in the killing fields of Cambodia, but one of the most puzzling footnotes in the slaughter and destruction of that country is the unsolved murder of the only British victim - the first Westerner caught up in the violence.

Gunmen burst into Scottish academic Malcolm Caldwell's Phnom Penh government guesthouse and shot him repeatedly in the chest and leg, killing him instantly. He was found with his apparent assassin slumped by his body and also riddled with bullet holes. At the time, the BBC reported he was killed by Vietnamese agents to discredit Pol Pot, but 30 years after the murder documents newly obtained by the Sunday Herald under the Freedom of Information Act reveal that the genocidal dictator himself ordered the assassination, early in the morning of December 23, 1978.

Just hours earlier, the 47-year-old father of four had met the despot, demanded to see deposed leader Prince Sihanouk and had asked about missing Cambodians and ministers, most of whom, it transpires, were already dead.

According to the classified documents, journalist Wilfred Burchett had seen an official Cambodian report a year later which said: "Caldwell was murdered by members of the National Security Force personnel on the instructions of the Pol Pot government."

An unnamed British civil servant adds: "Caldwell told Burchett he had every intention of asking some pointed questions and that he was absolutely determined to see Sihanouk.

"It is likely, therefore, that he upset his hosts, who were probably concerned that a prominent supporter/apologist of the Pol Pot regime might report in a critical vein on his return home.

"Matters probably came to a head after a private interview which Caldwell had with Pol Pot."

The papers also reveal a chilling account of the murder from eyewitness Richard Dudman, made five days later at the British embassy in Washington. The journalist for the St Louis Dispatch told officials of the moment a young gunman shot at him and Caldwell in the Khmer Rouge VIP guesthouse at 12.55am.

Born in Stirling into a middle-class Tory-voting household, Caldwell went on to get a double first at Edinburgh University by the time he was 21. He became a Marxist academic at London University's School of Oriental and African Studies and a left-wing activist, serving as head of CND in 1968-70.

A supporter of the Khmer Rouge, he was one of the first Westerners allowed into the country after 1975, and travelled to Cambodia with Dudman and fellow American journalist Elizabeth Becker just as the true horror of the genocide was becoming apparent.

Caldwell had spent three weeks touring the country surrounded by Khmer Rouge minders but had seen and surreptitiously photographed the impoverished peasants.

Dudman reported that in Phnom Penh he knocked on Caldwell's door as a young uniformed man appeared in the corridor with a machine gun on his shoulder and a pistol in his hand and fired at the two men. Dudman ran into his room and two shots were fired into the door. Then he heard more shots. 90 minutes later, a Cambodian security officer told Dudman that Caldwell was OK and he had to stay in his room.

But, Dudman then said, "An hour later a high ranking foreign office official told me Malcolm Caldwell was dead and asked me to witness the scene."

Dudman went to look and saw the open door of Caldwell's room and saw his dead body "supine, eyes wide open and body soaked in blood".

He estimated Caldwell had been hit at least three times. The official told Dudman that the dead gunman had shot Caldwell and then shot himself.

Becker's account indicates that the murder scene could have been staged. The Washington Post journalist found herself face to face with the killer and ran back into her room and hid in her bath.

After the shots, she then heard bodies being dragged up and down stairs on three different occasions. Dudman and Becker later noticed that there were bloodstains on the stairs and corridor.

The Foreign Office officials speculate that because of the time lapse and Becker's account, it was very possible that Caldwell's murder scene had been stage-managed.