Radovan Karadzic, the political leader of the Bosnian Serbs during the 1992-95 war and the architect of the worst atrocities in Europe for generations, is no longer a fugitive from justice. His capture means that he is virtually certain to become the first European to be found guilty of genocide.

This was a verdict denied to his former leader Slobodan Milosevic, who died in UN custody two years ago, at the International War Crimes Tribunal in The Hague, a venue now preparing to host Karadzic. His military sidekick, General Ratko Mladic, remains at large. Both men were masterminds of the campaign of terror and ethnic cleansing aimed at purging at least half of Bosnia of most non-Serbs. Both committed genocide against the Muslims of Srebrenica in July 1995.

There is, rightly so, rejoicing in European capitals at news of Karadzic's capture and the hope that this signals a new era for Serbia-European Union relations. But back-slapping should be put on hold until Mladic is also captured. The fact remains that it took 13 years to capture an overweight, middle-aged war criminal. It is not only legitimate, but a moral duty to ask why it took so long? And what does this say about Serbia's relationship with Europe. Already commentators are predicting that Belgrade's European Union aspirations will be helped by the capture. Other potential candidates for membership may see this as a possibly biased reaction. Turkey, for instance, will reflect that its membership hopes have been put on hold but it never had war criminals enjoying liberty on the streets of its capital.

Maybe this arrest does reveal that a more mature Serbia is fully ready to carry its responsibilities, but Mladic's continued freedom remains an insult to Europe's sense of justice and a moral challenge to Belgrade.