“Fake news” and propaganda have unfairly coloured the Khmer Rouge regime as a “genocidal” one, according to former Brother Number Two Nuon Chea, who claims there is simply not enough evidence to find him guilty of the “crime of all crimes”.

The word “genocide” has long been emblazoned on the entrance to the Khmer Rouge’s torture prison S-21 in central Phnom Penh, where 12,000 people – many of them cadres suspected of espionage – were slain by an increasingly paranoid regime.

Legally, though, the killings were not necessarily genocide. The term is defined as killings and other acts committed with the “intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such”.

In Case 002/02, the high-profile charge of genocide doesn’t refer to mass murder of the Khmer people; it only applies to two groups: Cham Muslims and the Vietnamese.

In what Chea’s defence lawyer Victor Koppe called “a precursor to today’s fake news”, the atrocities of the Khmer Rouge were exaggerated by a Vietnamese propaganda machine aimed at justifying their “invasion”.

This, he said, is part of a simplistic, reductionist narrative that – “much like a Donald Trump tweet” – is bolstered by media attention.

“[T]here is nothing in the evidence pointing to Nuon Chea having and sharing the intent to destroy, discriminate, exterminate or otherwise target the Cham or Vietnamese people,” he argued in a closing brief published this week. “[T]he gravity of the crime of genocide is reflected in the ‘stringent requirements which must be satisfied before this conviction is imposed’. None are met here.”

He argues very few witnesses provided evidence on how they were targeted, and when they did, “in most cases there was a legitimate reason for it unrelated to their membership in the Cham or Vietnamese group”. For example, when the Cham were targeted, the defence argued, it was because of their individual actions and rebellion, not because they were Cham.

“No matter how tempting it is to create legacy as the ‘Chamber who established the Cambodian genocide’, one must be cautious and resist the urge to convict Nuon Chea of genocide without proper legal basis.”

Prosecutor Nicholas Koumjian, however, said there was “no doubt” the Khmer Rouge leaders “intended to destroy the Cham and Vietnamese groups”. Tens of thousands of Cham and Vietnamese were allegedly killed during the regime.

“Where both defence teams go wrong is they confuse motive with intent. It does not matter if Cham and Vietnamese were killed because the [Communist Party of Kampuchea] saw them as rebellious or a threat, as long as they intend to destroy the group as such, their motive has no legal significance,” he said.

Professor Alexander Hinton, who testified as an expert before the tribunal last year, conceded that the “Cambodian genocide was highly politicised on all sides”, but that he nonetheless expected a guilty verdict to be handed down. “Genocide is political and so is its afterlife,” Hinton said.

“To say this, however, does not obviate historical fact. There is an enormous amount of evidence supporting the case that genocide took place in Cambodia, even when a narrow legalistic definition is used.”

The Khmer Rouge banned Islam, forbade prayer, burned Qurans and forced Cham people to eat pork and abandon their traditional dress. Had these policies continued, the prosecution argues, the Cham would have been destroyed.

Cham researcher Farina So agreed that “signs of genocide” against the Cham and Vietnamese appeared to take shape in the Khmer Rouge’s short but brutal rule.

“Immense and unimaginable suffering . . . is recalled by countless survivors,” she said, urging the court to deliver “meaningful justice” to survivors.

Nuon Chea has also urged the court focus on the “head, body and tail of the crocodile” – the head being Vietnamese imperialism and US bombing prior to 1975, the body being the Democratic Kampuchea regime and the tail being the consequences, in this case, the Vietnamese invasion that toppled the Khmer Rouge. In light of the whole “crocodile”, he argues, he cannot be found liable or guilty.

But historian David Chandler said that Chea had never denied he was second in command.

“This position cannot make him totally irresponsible for what happened under [Democratic Kampuchea],” he said. “Genocide may not be the right name for the horrors that ensued. I think crimes against humanity is a better phrase – but the defence is turning away from mountains of printed and recorded evidence to suggest that for over three years Nuon Chea was kind of standing on the corner watching a weird parade.”

War correspondent Elizabeth Becker said there was “no question that Nuon Chea had the power and authority to oversee the regions of Cambodia”.

“The tribunal has amassed ample evidence of the murderous behaviour of Democratic Kampuchea. That is the permanent record that Cambodians themselves have created. It is not propaganda devised by the Vietnamese.”

While genocide might dominate the public imagination, Koumjian pointed out that in terms of sheer numbers of victims, the far bigger crimes are the enslavement of millions and the killing of hundreds of thousands of Khmer people – “even if those killings don’t meet the technical legal definition of genocide”.