Terrible things happen in all wars. The deaths of combatants and fatalities among civilians are impossible to avoid without the overwhelming victory of one side and the early surrender of the vanquished. In a conflict like that in Ukraine, however, where the defenders have not only held back the aggressors but even forced them to retreat, the casualties will inevitably be high, especially in besieged cities like Mariupol.

But in addition to the appalling impact on civilians of the seemingly indiscriminate bombardment of their homes and shelters, stories are emerging of atrocities committed against the population. Men have allegedly been found shot dead with their hands bound. Mass graves are said to contain the bodies of dozens of civilians murdered by Russian forces. There are always accusations of this sort: the Russian claim that Ukrainian far-Right militias were carrying out atrocities in the Donbas was one of the reasons given by Vladimir Putin for staging the invasion. He said he wanted to prevent “another Srebrenica” and yet is presiding over precisely that, of occupying forces using terror and violence not merely to intimidate local people but almost for the sake of it.

The depravity is on a par with anything seen in modern warfare and has echoes of the butchery that took place in the same corner of Europe during the Second World War. On one street in the town of Bucha the bodies of dozens of civilians can be seen, apparently shot dead by the retreating Russians. The Kremlin has greeted almost every criticism of its gratuitous destruction in Ukraine as exaggerated or accidental or even staged by the defenders themselves. But Putin and his advisers cannot hide from the consequences of their actions any more than the Nazis or Bosnian Serb warlords could for theirs.

War crimes investigators should go to Ukraine as soon as it is safe for them to do so to gather evidence about what has happened. Since the Russian forces have largely withdrawn from the areas where atrocities have been witnessed this could be done quickly. A case needs to be constructed that will damn Putin in the eyes of even those parts of the world that remain ambivalent towards his belligerence.

Proving war crimes might not lead to any prosecution since detaining those responsible will be impossible if they remain in Russia. But we can make sure they are never able to travel anywhere else again without risk of arrest and trial.