Earlier this the year, Sri Lanka’s long-running civil war culminated in the military destruction of the Liberation Tigers of Tamil Eelam in a hideous gotterdammerung in the islands’ north-east.

For the most part, the world discreetly hid its eyes from exactly what took place, an evasion made easier by the Tigers’ own unlovely history (suicide bombings, cult of personality, etc). Last week, however, Britain’s Channel Four shattered that polite silence by screening a particularly ghastly video (warning: it’s NSFW — or anywhere else for that matter), purportedly taken during the war’s final stages.

The clip shows a naked man, hands tied behind his back. He’s thrown to the ground in what seems like a jungle clearing. A second figure dressed in Sri Lankan military uniform gives the prisoner a final kick and then fires an assault rifle into his head. As the body slumps, there’s a giggle. “It’s like he jumped,” says a voice. The camera pans, revealing a landscape strewn with corpses: most of them naked, all of them bound. Later, a second man is dragged out. He, too, is shot.

According to Channel Four, the footage came from the exile group, Journalists for Democracy in Sri Lanka. JDS says the clip, filmed on a mobile phone in January during the battle for the LTTE’s capital Kilinochchi, had been circulating amongst soldiers, a grisly digital souvenir.

For its part, the Sri Lankan government has denounced the footage as fraudulent. The Tigers often dressed in army uniforms, explained military spokesman Brigadier Udaya Nanayakkara. Why, they probably made the clip themselves.

Well, it’s a theory. But does the brigadier encourage journalists to investigate, to clear up the imposture? No, not so much. In fact, yesterday, the Sri Lankan high court sentenced prominent editor JS Tissainayagam to 20 years hard labour. Tissainayagam, among other sins, had published details of war time atrocities — and, in many respects, he got off lightly. The advocacy group Reporters Without Borders lists Sri Lanka as the country in which media employees are most likely to disappear. That, incidentally, explains Journalists for Democracy in Sri Lanka: not a Tamil group but an organisation made up of some of the many journalists forced to flee for their lives.

Despite the government’s phoned-in denial, the massacre footage seems authentic precisely because it’s so uncinematic, so understated. There’s no great explosions, no gouts of blood, just one group of young men systematically and unhurriedly murdering another. The childishness of the soldiers (in bumpkin Sinhala, they play out the game “kurupiti gahanawa wage” “Your Turn, My Turn” — as they kill) recalls other battlefield atrocities from other conflicts, where banality and routine normalises the unspeakable and steadies the executioners. The victims’ empty expressions, the rubberiness of their limbs: you can see something similar in the few surviving photos of the Einsatzgruppen in Poland, in which the process of mass slaughter seems to reduce its victims almost to automatons even before any shots are fired.

As for the circulation of a video, that’s a recent technological innovation in group violence, popularised only over the past decade or so. You’ll recall that someone captured Saddam’s last moments on a cellular phone, that, in Iraq, US soldiers regularly swapped combat footage until their commanders cracked down on the practice. Sharing the moments of death bonds the perpetrators and dissolves their responsibility, with any lingering unease diffused among everyone who approvingly nods along to the atrocity.

In any case, the most obvious reason to think the JDS footage authentic is that there’s so much other evidence suggesting that terrible things took place in the war’s final phases. With the Tigers confined to a shrinking scrap of jungle, the Sri Lankan government launched a full-scale assault, using mortars and artillery. The conflict zone at that time contained hundreds of thousands of ordinary people but the same military mouthpieces that so airily dismiss the massacre clip assured the world that no innocents were killed. By contrast, a Times investigation put the toll at about 20,000.

And still the abuses continue. Hundreds of thousands of civilians remain in militarised detention centres, where they lack proper sanitation and medical care, and where the few external observers reliably report ongoing intimidation and abuse. When United Nations Secretary General Ban Ki-moon visited camps in May, he said: “I have travelled around the world and visited similar places, but this is by far the most appalling scene I have seen.”

In some ways, the worst thing about watching that JDS clip is the despairing sense that it will change nothing. In the wake of atrocity, we’ve all heard the Sri Lankan rhetorical style, time after time — in Iraq, in Afghanistan, in Gaza. These days, such things can simply be brazened out. On the one hand, there’s blackened bodies and witness testimony and video evidence; on the other, there’s a square-jawed military man on the TV, saying, “Who are you going to believe, me or your lying eyes?”

Cruelty and abuses spread like viruses, with the standards set by the wealthier nations impacting disproportionately on the earth’s wretched. To put things bluntly, if the urbane and sophisticated Barack Obama, liberalism’s shining knight, won’t punish his employees for torture (as well as the waterboarding and the stress positions and the sleep deprivation, the CIA, we now learn, threatened detainees with mock executions, power drills and sexual assault), why should anyone expect Sri Lanka, an impoverished Third World Government grappling with a savage war, to investigate extrajudicial killings? Amnesty and similar bodies can produce as many reports about the internment camps as they like but after nearly a decade of politicians from Great Britain, the United States and, yes, Australia routinely dismissing the “rights agenda” as shrill and hysterical on Guantanamo or Bagram or refugees or anything much else, there’s very little in the way of political repercussions if Brigadier Udaya Nanayakkara simply shrugs his epauletted shoulders at a massacre or two.

So that, unfortunately, is where we’re at, a decade into the 21st century: a jungle clearing, a scattering of bodies — and, almost certainly, no consequences whatsoever.