There’s a lot that is unclear about the fate of the three captured fighters – two of them British – who were sentenced to death in Donetsk on Thursday. Even the charges are obscure. All that’s obvious is that the authorities are trying to evade the Geneva conventions. It’s illegal to punish people simply for fighting, so Shaun Pinner, Aiden Aslin and Saaudun Brahim were charged with other crimes instead. They were accused of terrorism, mercenarism and attempting to topple the government. According to laws adopted unilaterally when Donetsk declared itself independent of Ukraine in 2014, that means they can now be shot by a firing squad. What’s more, the “trial” in Donetsk sends out a deeply worrying message about the future: not just concerning the course of the war, or relations between Russia and the west, but the very international legal frameworks that the world has tried to uphold since 1945. The allegations are inherently weak, in that all three men were serving with Ukraine’s army when they were captured in Mariupol. Even if they are taken at face value, though, the procedure to weigh up guilt was blatantly unfair. It’s not certain that the defendants had independent legal representation, let alone the quality of advice that is appropriate in a capital trial. Despite that, they were invited to plead guilty at their first appearance and sentenced behind closed doors within 24 hours. That’s not due process, it’s the kind of judicial procedure that gives rubber stamps a bad name. The men have already announced plans to appeal, and if that fails, they’ll be petitioning the head of the Donetsk People’s Republic for a pardon. But it’s not in eastern Ukraine that decisions about the case will be made. Though the Kremlin recognises the region as a sovereign state – unlike every other government in the world – its independence is fictional. And now that Russia’s proxies in Donetsk have condemned British prisoners to bargain with, Moscow is clearly looking forward to ramping up the pressure on London. The Kremlin’s spokesperson said, even before the men were sentenced, that Britain might need to discuss the case with Donetsk – observing that this would amount to recognition of its independence. Responding to complaints by foreign secretary Liz Truss that the trial was a “sham”, Russia’s foreign ministry has observed that the British reaction to such cases is “often hysterical”. That’s cynical enough. Though Russia was required to comply with the Geneva conventions when it took custody of captured prisoners in Mariupol, it clearly allowed the three defendants to be transferred to Donetsk – thus facilitating the improper death sentences that have just been handed down. But those sentences are a sign of worse to come – because it’s looking as though Russia plans to stage a grander judicial spectacle it can call its own. That’s been the plan from the start. When Putin announced Ukraine’s invasion, he promised not just “demilitarisation” and “denazification” but also trials for everyone “who perpetrated numerous bloody crimes against civilians”. At least a thousand of the fighters who surrendered at Mariupol are already in Russia, under “investigation”, and a show trial seems to be imminent. Russian media outlets are reporting that some captured fighters have swastika tattoos and dubious social media postings to account for. A law going through the Duma proposes to ban prisoner exchanges, so that “Nazi criminals” aren’t able to evade justice. One deputy has called for Russia to resume the death penalty – last used in 1996 – so as to eradicate the “beasts in human form” it now has in its custody. Legislators and state-sanctioned media commentators are predicting a judicial spectacle like that seen in Germany after 1945 – a “Nuremberg 2.0”. The promise is as ominous as it sounds. The denazification trials of postwar Germany always had two sides. They claimed to demonstrate that unprovoked violence is always punishable, and asserted that states can’t act just as they please. As far as Stalin was concerned, however, the trials were displays of force (so much so, that the man he appointed to judge Nazi leaders had previously ordered the execution of many of his Communist rivals), and it’s that darker tradition that is now about to be revived. As and when Nuremberg 2.0 begins, it won’t be an investigation into war crimes so much as a show trial. That doesn’t bode well for the three defendants who are now on death row in Donetsk – but the potential consequences could be a lot worse. The erratic prosecution of war crimes has provoked controversy for decades. There has been a failure to enforce grave breaches of international law in places from Bosnia and Kosovo to Israel, Iraq and Syria. But perspectives are suddenly diverging far more radically. With western nations and Russia accusing each other of the same crimes they defined and prosecuted together in 1945, the minimal compromises that allowed humanitarian law to develop over subsequent decades are falling apart. The purpose of denazification was originally to show that unprovoked violence had become impermissible. Whoever gets convicted or executed in the weeks to come, that shared aspiration is now history, in every sense. Sadakat Kadri is a barrister at Doughty Street Chambers and author of The Trial: A History from Socrates to OJ Simpson