Former Khmer Rouge leaders Nuon Chea and Khieu Samphan sat impassive in the dock as the final verdict in Case 002/01 was handed down to them yesterday, in what was widely described as a “historic” moment for the Cambodian people and international law.

The two elderly defendants, who were initially convicted of crimes against humanity in 2014, yesterday had their appeals of those convictions rejected and their life sentences upheld by the Supreme Court Chamber at the Khmer Rouge tribunal.

Though neither Chea nor Samphan had “committed any of these crimes with their own hands, they were, nevertheless, criminally responsible for them”, the judgment read, noting they had planned, instigated, aided and abetted, and – in Chea’s case – ordered those crimes.

While the Supreme Court Chamber upheld many of the convictions for crimes committed by the brutal regime’s Brother Number Two, Chea, and head of state, Samphan, its appeal judgment at times was unsparing in its criticism of multiple errors made by the lower trial chamber.

Both had their convictions for “extermination” overturned, while convictions for murder and political persecution were also reversed in relation to the crimes that took place at Tuol Po Chrey, where at least 250 soldiers from the ousted Lon Nol regime were slaughtered.

Though the Supreme Court Chamber found crimes against humanity had in fact occurred in Tuol Po Chrey, it found insufficient evidence for Chea, 90, and Samphan, 85, to be held responsible for them.

The convictions of murder, persecution and “other inhumane acts” stemmed from the forced evacuation of Phnom Penh on April 17, 1975, and a subsequent second phase of mass population transfers.

One conviction on the charge of extermination was stripped from the second phase of forced displacements, though the Supreme Court Chamber instead found Chea and Samphan guilty of murder in that instance.

It was a judgment that Khieu Samphan defender Anta Guisse branded “cosmetic justice”.

“People will say these are simply words of a bitter defence, but actually no, we are lawyers, and issues of law are essential,” she said. “It is always very frustrating to see that a symbol erases rights and laws, and we feel this on behalf of Khieu Samphan.”

Nuon Chea’s defence lawyer, Victor Koppe, said he was adopting “a milder tone” than that of his vehement denunciations of the court in the past, but stood by his assessment of the appeal as “irrelevant” due to what he described as the trial chamber judges’ “deep bias” and “incompetence”.

The Supreme Court Chamber’s decision did appear to partly vindicate Koppe by criticising the trial chamber’s decision not to call as a witness Heng Samrin, a former Khmer Rouge cadre and the current president of the National Assembly. His exclusion, the judgment said, was both “unreasonable” and “erroneous”. Samrin’s presence at the court had been requested by Koppe several times during the trial.

“Who was responsible for the implementation for the decision to evacuate [Phnom Penh]? Heng Samrin,” Koppe said yesterday. Koppe added that he had discussed the findings with Nuon Chea and “couldn’t explain to him” why a life sentence was still in place.

Despite the convictions for Tuol Po Chrey being overturned, Marie Guiraud and Pich Ang – lawyers representing victims of the regime – said that the 20 civil parties admitted to the case because of loved ones killed at Tuol Po Chrey were also victims of other crimes, and the civil parties as a whole were satisfied with the life sentence.

About 100 civil parties were present for yesterday’s judgment. However, more than 100 have died since the beginning of the trial, which has dragged on for years after its initial projected completion date.

For several prominent Cambodians, the reaction was mixed. Referring to the many current leaders – including Prime Minister Hun Sen – who held senior roles in the Khmer Rouge, prominent disabled people’s rights activist Ngin Saoroth said he “wanted to see more politicians accepting the actions that they had committed in the past”.

Without that, he said, the trials were “only theatre”.

Yang Sang Koma, founder of the Cambodian Center for Study and Development in Agriculture (CEDAC), lost his father and siblings to the “savage” regime. “Justice is not yet complete since only a few leaders were prosecuted. I want to know more of the truth,” he said.

Legal expert Sok Sam Oeun, however, said he remained “unclear” as to Khieu Samphan’s guilt, saying “in the regime, some leaders were also under pressure”.

Despite the tone of finality yesterday, the road to justice is long from over. Case 002/01 is complete, but the case’s second phase – Case 002/02 – continues, with hearings expected to finish in January 2017.

Prosecutor Nicholas Koumjian said a life sentence was no reason to suspend the prosecutions of other serious crimes that affected the majority of the victims, including internal purges, the forced marriages of tens of thousands of couples, rape within those marriages and the alleged genocide of the Vietnamese and the Cham.

Koppe, however, said the bar for evidence had been raised significantly thanks to the appeal, and hinted the prosecution would struggle to find evidence for the genocide charge, which he said was “very sketchy”.

Koumjian, nonetheless, called the case “the most important trial, at least since Nuremburg, involving the most horrendous crimes since the Second World War” – a sentiment echoed by David Scheffer, the UN secretary-general’s special expert for the tribunal.

“The long arm of international justice can prevail,” Scheffer said, urging governments in the Philippines, South Sudan, Syria and North Korea to “take note”.

“International criminal law is not backing down, it is forging ahead.”