Timothy Garton Ash is a historian, political writer and Guardian columnist. His personal website is www.timothygartonash.com.

At last they've got him. There's not much good news from Europe at the moment, but the fact that Ratko Mladic is now sitting in the detention cell of an international tribunal in the Hague is a cause for unqualified celebration. The man directly responsible for the massacre of 8,000 unarmed men and boys at Srebrenica will now be held to account for that and other atrocities. This is another step forward in one of the great developments of our time: the global movement towards accountability.

Just over 60 years ago, the Polish poet Czesław Miłosz wrote a poem addressed to the torturers and mass murderers of one of the bloodiest periods in European history. "You who harmed an ordinary person," he warned, "… do not feel safe." People may heap sycophantic praise on you now, but "the poet remembers", poeta pamieta.

Back then, that was about all your mass murderer had to be frightened of: the poet remembering. A post-1945 moment of very imperfect international accountability, symbolised by the Nuremberg trials of Nazi leaders and the founding treaties of international humanitarian law, had faded behind the iron curtains and instrumental amnesias of the cold war. Even the most basic facts about many atrocities were systematically concealed or falsified. Monsters died in their beds, with their medals still hanging from the uniform in the wardrobe. Only the poet remembered; the poet, and the ordinary person, if still alive.

But those post-1945 ideals never quite died...