Two former officers of Cambodia's Khmer Rouge were arrested and charged today with the murder of a British mine clearance expert.

The two men, Khem Ngun and Loch Mao, were once deputies of Ta Mok, one of the Khmer Rouge's most brutal chieftains, and the “Butcher” thought responsible for numerous massacres during the Pol Pot years.

Christopher Howes and his Cambodian interpreter were kidnapped and slain in 1996 as they risked their lives to rid the wartorn country of deadly landmines.

Snatched by guerrillas in the final, dark days of Pol Pot's life, their fate was not properly known for two years after the incident took place.

Investigating detectives sent out to Cambodia by Scotland Yard later gathered evidence that Howes and Huan Huot had led a group of 20 local Mines Advisory Group helpers to a notoriously mine-strewn zone north of the Angkor Wat temple complex.

The whole group was taken captive and Howes was offered the opportunity to leave and find enough money to pay a ransom. He refused, and managed to talk his captors into sparing the lives of his colleagues. But Howes himself and his interpreter were taken deep into the mountain territory still controlled by the Khmer Rouge, where they were killed soon afterwards.

Witnesses identified Ngun as having given the order for the killings, and it is for that he will now stand trial in Phnom Penh.

If found guilty, the two face up to 20 years imprisonment for premeditated murder, and a further ten for kidnapping. The trial follows years of diplomatic pressure on Phnom Penh to bring to justice surviving former leaders of the Khmer Rouge.

Although they were identified as the alleged culprits many years ago, Ngun and Mao have thrived for many years in Cambodian society - the former rising to become a major general in the Cambodian Army, the latter working as a senior civil servant.

At the critical moment in 1998, when they might otherwise have been arrested, the Cambodian Government was hoping to encourage defections from the last remaining Khmer Rouge strongholds. It was as part of that controversial policy that Ngun and Loch Mao managed to slip through the net.

Even for a nation brutalised by the “killing fields” horrors of Pol Pot, the murder of the British mine-clearance expert caused widespread public shock. A street in Phnom Penh is named in Howes's honour.

This week, 76-year-old Khieu Samphan, who was nominally the head of the Khmer Rouge in the 1970s, arrived in the Cambodian capital, where he is expected to stand trial for crimes against humanity in a tribunal backed by the UN. Pol Pot himself died in the jungle nine years ago but four senior members of his regime are now awaiting trial as the UN tribunal seeks justice for the 1.7 million people killed under the Khmer Rouge regime.

Following the death last year of Ta Mok, investigators say that they are running out of surviving top-level Khmer Rouge chiefs - men seen as vital information sources in building an accurate picture of the regime's atrocities.

Samphan is unique among former regime bosses in having written a book on Cambodian history under the Khmer Rouge: “Cambodia's Recent History and the Reasons behind the Decisions I Made.”

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