BANGKOK, Thailand -- Defending Pol Pot's Khmer Rouge leaders at an international tribunal may include arguing about genocide and the lack of a "smoking gun," despite the deaths of up to three million Cambodians, according to U.N. Principal Defender Rupert Skilbeck.

"One of the big questions will be whether, what happened in Cambodia, was genocide or not," Mr. Skilbeck said in an interview.

"There is a very strong legal argument to say that genocide is when you kill people because of their ethnicity, whereas the vast majority of the [Khmer Rouge] purges were not for ethnic reasons, but were for political reasons. So genocide may not be possible" as a successful prosecution charge.

Mr. Skilbeck heads the Defense Support Section of the tribunal, which is officially called the Extraordinary Chambers in the Courts of Cambodia (ECCC).

A London-based criminal lawyer, Mr. Skilbeck was previously Defense Advisor for the Special Court for Sierra Leone, and head of the Criminal Defense Section for the War Crimes Chamber in Sarajevo.

The ECCC is gearing up in Cambodia to put on trial a handful of elderly Khmer Rouge leaders, almost 30 years after their 1975-79 "killing fields" regime was toppled.

Khmer Rouge communist leader Pol Pot died in 1998.

Nuon Chea, who was Pol Pot's second-in-command, distanced himself from charges of mass murder when he told Cambodia's Phnom Penh Post newspaper in January: "Why should we have killed our own people? I do not see a reason.

"We wanted a clean, illuminating and peaceful regime," Nuon Chea, 80, said.

The number of Cambodians who died from executions, torture, starvation, disease and slavery under the Khmer Rouge is usually pegged as 1.7 million people, but the ECCC's Web site said "more than three million people perished" during to the regime's fanatic, back-to-the-jungle administration.

The surviving Khmer Rouge leaders, who reside in Cambodia, could defend themselves in various ways, Mr. Skilbeck said.

"There has to be a discussion about whether there was an international armed conflict or not," he said, because the Geneva Conventions are rules for armed conflict, which can differ for acts during peace or domestic unrest.

Pol Pot seized power after Cambodia's U.S.-backed leader Lon Nol flew to California, and Washington lost its regional Vietnam War which included massive U.S. bombardment of the impoverished Southeast Asian nation.

America is not financially supporting the tribunal which is mostly funded by Japan and Europe, with help from India, New Zealand, Australia and others.

U.S. officials "made it very clear they will fund it, but only when they are sure it is going to be a fair process," Mr. Skilbeck said.

On November 26, 1975, seven months after Pol Pot's victory, U.S. Secretary of State Henry Kissinger said to Thai officials: "You should also tell the Cambodians that we will be friends with them. They are murderous thugs, but we won't let that stand in our way.

"We are prepared to improve relations with them. Tell them the latter part, but don't tell them what I said before," Mr. Kissinger said, according to a previously "secret" transcript recently published by the U.S. National Security Archive.

"Seven to 10 defendants," all elderly Cambodians, may stand trial at the ECCC, Mr. Skilbeck said.

Only one, Mr. Duch (pronounced: "doyk") -- who ran Phnom Penh's Tuol Sleng torture chambers -- is in jail. No arrest warrants have yet been issued to apprehend any others.

"The vast majority are living openly in houses, whether they are in Phnom Penh or in different places around the provinces.

"Some have been clearly identified as likely accused, so there is no secret about some of them. Some people perhaps won't be expecting a knock on the door. We will have to see what happens when they start to arrest people," Mr. Skilbeck said.

Cambodia abolished the death penalty.

"Anyone convicted of large-scale atrocity crimes is likely to get a sentence for the rest of their life," the U.N. Principal Defender said.

"The first trial starts sometime during next year. We will probably get a verdict before the end of next year...maybe the beginning of 2009. If there are any subsequent trials to that, it will probably take about six months each, so they'll come in six-month intervals after that."

Mr. Skilbeck said there is "no smoking gun," or single piece of evidence to convict the Khmer Rouge.

"There is no instance [on record] where the decision was made to make killings. There are no documents directly ordering large-scale atrocities to occur.

"So the prosecution, as often happens, will have to...piece together their case from lots of different people's evidence," the head of the ECCC Defense Support Section said.

r. Skilbeck is tasked to support the Khmer Rouge's defense lawyers -- foreign and Cambodian. He does not personally defend the accused, or wield veto power over the lawyers.

"My job is really to organize the defense, and to get it ready, and to make it happen.

"I will get all the individual defense lawyers to do the cases. Once we've got them up, and they are able to do the cases, we will give them back-up legal support to help them do the job," he said.

"Foreign or Cambodian, they will be independent, only subject to the court's ability to discipline them if they get out of line during the courtroom hearings."

Richard S Ehrlich is a Bangkok-based journalist who has reported news from Asia since 1978 and is co-author of "Hello My Big Big Honey!", a non-fiction book of investigative journalism. He received Columbia University's Foreign Correspondents Award, and his web page is