The last surviving senior leader of Cambodia’s radical Khmer Rouge regime has had an appeal against his conviction for genocide rejected at a war crimes tribunal in the capital Phnom Penh.

The ruling on Thursday in the appeal of Khieu Samphan, 91, the former head of state of the 1975-1979 “Democratic Kampuchea” government, marks the final decision by the court and ends 16 years of work by the UN-backed war crimes tribunal.

Thursday’s ruling is expected to be the last by the tribunal, which brought to justice just five senior Khmer Rouge leaders – including one who died during proceedings and another who was ruled unfit to stand trial – at a cost of more than $330 million.

Khieu Samphan – who is now the sole remaining leader of the regime who is behind bars – was once known as the ‘Mr Clean’ of the Khmer Rouge, a hardline Communist regime under which two million people perished in fewer than four years.

Though Khieu Samphan and his legal team were unable to convince the judges that he was innocent of genocide, he appeared to have convinced himself — despite being found guilty of crimes against humanity in a separate case before the tribunal in 2014.

Guilt, Khieu Samphan said, was assigned to him as a symbol of the regime and not for his deeds as an individual.

As Short notes, Khieu Samphan was one of only two Khmer Rouge leaders Pol Pot had ever singled out for praise publicly.

There have been so few convictions for genocide in history,” said Etcheson, who had spent four decades investigating, uncovering, documenting and holding to account those responsible for crimes during the Pol Pot regime.

From 2006-2012, Etcheson was also an investigator with the office of the co-prosecutor at the war crimes tribunal — whose official name is the Extraordinary Chambers in the Courts of Cambodia (ECCC).

Commenting on Khieu Samphan’s apparent inability to admit to his role in the crimes of the regime, Etcheson said it would be difficult and possibly “treacherous” to attempt to contemplate what was going on in Kheiu Samphan’s mind.

While the effectiveness of the court will be debated for years, Etcheson said he felt a “sense of accomplishment” knowing that justice was done in the case of the Khmer Rouge leaders convicted, and that the investigation “put the fear of god” in those identified as war criminals but whose cases did not proceed to trial.

Support was also needed for the thousands of survivors and victims of the Khmer Rouge who joined the tribunal as civil parties — a first for a war crimes court — and provided testimonies.

He pointed out that it took a staggering $300m and more time for the Cambodian tribunal to convict three Khmer Rouge leaders than it took the United States, the United Kingdom and France to put on trial 5,000 war criminals following World War II.

Asked who would have an interest in revising what had occurred during the Pol Pot regime, and what was uncovered by the war crimes court, Maguire said: “Well, I think, of course, the Chinese and Cambodian government.”.

“We will continue to do that,” he said, adding that reporters will one day contact Cambodian scholars of the Khmer Rouge regime – an area of research that was initially led by foreign researchers