Earlier this month, two former leaders of the Khmer Rouge, a murderous group that briefly ruled Cambodia in the 1970s, were convicted of genocide. The ruling was the first verdict on genocide by the tribunal, which is hearing KR-related cases. It’s also likely to be the last; not because there are no more crimes to be investigated, but because Cambodia’s leadership wants the tribunal to go away. That’s a mistake. Justice is needed today more than ever; no national leader should ever think that he or she can escape an accounting for their actions.

From 1975 to 1979, the KR ruled Cambodia. Led by Pol Pot, the nom de guerre of Saloth Sar, they sought to re-create their country as a self-reliant agrarian nation. They tortured and executed enemies — real and imagined — along with their families, as well as anyone they considered “tainted”: Wearing eyeglasses was enough to warrant that label. As many as 2 million people, about one-quarter of the population, died from murder, overwork or starvation.

That madness and the resulting instability prompted the Vietnamese to invade in 1979. They installed a former KR leader named Hun Sen as head of the new government; he remains in power to this day, a testimony to his guile and ruthlessness. The KR fought a low-level insurgency for over a decade, but the movement faded as thousands of its supporters defected to the government.

In an attempt to provide justice to KR victims, the Extraordinary Chambers in the Courts of Cambodia (ECCC) was established in 2006 with both Cambodian and international judges. In the nine years since it was set up, it has convicted three people for atrocities committed by the Khmer Rouge regime. Kaing Guek Eav, known as Duch, was in charge of the Tuol Sleng torture center and prison in Phnom Penh. He was convicted in 2010 and is serving a life sentence. Head of state Khieu Samphan and deputy Nuon Chea were sentenced to life in 2014 for crimes against humanity. (One other defendant died before a verdict was rendered and another was found mentally unfit for trial.)

Khieu Samphan and Nuon Chea faced a second set of charges, this time for genocide, based on allegations that they had tried to exterminate the Cham Muslim and ethnic Vietnamese communities in Cambodia. Over a third of the Cham population (300,000 people) died while nearly all the Vietnamese were deported, and the 20,000 who stayed were killed. (In their second trial, they were also found guilty of crimes against humanity of murder, extermination, enslavement and torture.)

The genocide finding is important because the Cambodian killings were horrific, but it was not clear that the KR leadership had the required “intent to destroy, in whole or in part, a national, ethnic, racial or religious group.” The ruling eliminates those doubts and establishes the historical record.

The ruling was widely applauded. Youk Chhang, executive director of the Documentation Center of Cambodia, called acknowledgement that genocide occurred “a historical moment for Cambodia.” Adama Dieng, U.N. special adviser on the prevention of genocide, said the convictions showed that “justice will prevail, and that impunity should never be accepted for genocide and other atrocity crimes.” Japan’s Foreign Ministry called the verdict an “additional achievement of (the ECCC’s) judicial process,” a “crucial step toward the conclusion of the entire peace process in Cambodia” and the strengthening of rule of law in the country.

Unfortunately, the ruling is likely to be the last, given intense hostility to the tribunal. Some critics charge it is a waste of money, having spent $300 million over nine years to secure just three convictions. More significant, though, is the objection of the Cambodian government. The court has Cambodian and international judges, and Prime Minister Hun Sen has used his influence over Cambodian jurists to influence its decisions. Officially, Hun Sen says he wants to look forward, not back, and move on from the KR era. Human rights experts counter that he fears active pursuit of its mandate could ensnare him and his allies.

Japan has been deeply involved in Cambodian politics since it oversaw the peace process and transition to democracy in the early 1990s. It has contributed more than $2 billion to various projects, and earlier this year it agreed to provide more than $90 million for economic and electricity projects. Japan should press Phnom Penh to continue its pursuit of justice, to protect the integrity of the tribunal and the human rights of the Cambodian people. The documents created by and for the tribunal must be preserved to ensure there is a historical record.

This effort matters not just to Cambodians but to other regional governments that might contemplate similar actions. The military in Myanmar is paying attention to what transpires in Cambodia. It must not think that it can commit atrocities with impunity. Justice in Cambodia will show that it cannot.