Nato in Kosovo: The legal view - Only sanctions will force out Milosevic's gang

Serbian leaders and soldiers must be put on trial for the crimes they have committed against humanity

When Richard Dimbleby told the world about the horrors of Belsen concentration camp, there were victims still alive to testify against political criminals rounded up as the allies advanced. Today the BBC broadcasts from the mass graves and torture centres of Kosovo, mocked by the unrepentant perpetrators of these crimes against humanity as they drive to safety in Serbia.

There can be no peace without justice, and the moral purpose of this war has been betrayed by the Nato diplomats who failed to insist, as a condition for stopping the bombing, on Serbian surrender of its war-crimes suspects.

This was, after all, a war aim clearly and repeatedly stated by the British Prime Minister. Yet today, as investigators and forensic scientists begin the long and laborious task of disinterring and then identifying the bodies, the prospect of ever bringing their murderers to justice seems remote. There they go - lorryloads of Serbian soldiers, gesturing obscenely at bereaved families and shouting defiant confessions to the number of Kosovars they killed.

In any sane world, they would all be in custody - under interrogation and on identity parades. Instead, they go back to protect their leader, Slobodan Milosevic, and their army's high command from facing the indictments that await them in the Hague courtroom.

Nato deliberately and disastrously omitted any provision for justice from the peace accord brokered by the naive Finnish president, Martti Ahtisaari. There was a specific clause in the Dayton agreement of 1995 (which ended hostilities with the Bosnian Serbs) requiring co-operation with the Hague tribunal: this embarrassed Nato as it consistently refused to order the arrests of indicted leaders such as Radovan Karadzic and General Ratko Mladic.

Its fear, ironically, was that any trial might reveal them as puppets of Mr Milosevic, the real architect of ethnic cleansing in the Balkans, whose impunity was regarded as necessary for negotiations.

But it is too early to despair of retribution, at least for the Serbian leaders who are principally responsible for the mass graves. International criminal law has a principle of "command responsibility" established in the case against General Yamashita, whose Japanese troops committed similar outrages in the Philippines at the close of the Second World War. Leaders who connive at mass killings - by failing to stop them or taking no action to prevent them - are as guilty as those who directly order them. This is the legal basis for the indictment of Mr Milosevic and his five top generals. The international arrest warrant will mean that they must skulk all their lives in Serbia, or find a Baghdad bolt-hole.

But there is a means of levering them to justice, if politicians have the resolve to employ it. Sanctions work slowly, but surely - as the determined Lockerbie relatives found recently. Even more remarkable was how they worked on Croatia, which refused to surrender its war crimes suspects - until last year, when America made this a condition of a much-needed loan.

Public fury aroused by the unveiling evidence of systematic torture and mass murder must now force Nato governments to make it an unbreakable condition that not a pennyworth of aid or reconstruction assistance of any form should go to Serbia unless and until President Milosevic and his indicted commanders present themselves for trial. The UN's economic and financial sanctions in particular, which brought Libya to its knees, must be directed at Serbia, with some hope that self-interest will produce a compliance with international law.

But is it ethical to punish a people for the wickedness of their leaders or their soldiers? When he Hague tribunal was set up, many argued that it would demonstrate how war crimes were committed only by individuals, thus relieving their countrymen from the stigma of "collective responsibility" for crimes against humanity. This idealistic notion has been called into question - first by historians who revealed just how many Germans were "Hitler's willing executioners", and now by evidence of widespread awareness and support in Serbia for the "ethnic cleansing" of Kosovo. The continuing punishment of the Serbian people is justifiably imposed for their general complicity in the Kosovan barbarities: it can be remitted when they show a sense of shame by surrendering the Milosevic gang.

In the meantime, convoys of Mr Milosevic's willing executioners are escaping, protected by our troops from the Kosovars they loudly regret they did not kill. Their time may come. A few will be identified as members of death squads, and indicted: their surrender will be possible if it is made the eventual price of their country's prosperity. Milosevic and his generals will keep for a few years yet, and the evidence for their command responsibility will mount. One feature of a crime against humanity is that it can never be forgiven - as Generals Pinochet and Galtieri (under indictment in Argentina) are discovering in their dotage. The Peace Agreement failed to deliver justice, but it can come in the fullness of time so long as we maintain our rage against the men who fill mass graves.

Geoffrey Robertson QC is author of `Crimes Against Humanity - The Struggle for Global Justice', published by the Penguin Press next week