In the autumn of 1991, a Serbian politician named Vojislav Seselj arrived in the city of Vukovar, on the Croatian side of the River Danube. Serbian militias were attacking Vukovar, intent on expanding the borders of their state. Under Yugoslavia's communist regime, Seselj (pronounced "Sheshel") had been imprisoned for his nationalist views. Now, as the Yugoslav Federation split and ethnic nationalism became the guiding principle of politics, he had become a hero. He'd come to Vukovar, then being "cleansed" of Croats, to raise morale among the Serbs, to make speeches and to enrol members in what would come to be called the Serb Radical party, which he would come to lead.

This much is undisputed. Everything else is. And it's the everything else that is now grinding its way through a big grey building in the diplomatic quarter of The Hague, the Netherlands' seat of government. The building is the International Criminal Tribunal for the former Yugoslavia (ICTY). It is the place where former Yugoslav president Slobodan Milosevic was tried, and where - in a prison nearby, in March 2006 - he died of a heart attack. It is also where wartime Bosnian Serb leader Radovan Karadzic, whose arrest was announced this week, is expected to be tried. The ICTY is the expression of a great, end-of-communism hope: that justice could be international, and that evildoers would have no hiding place.

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Around the time Seselj was in Vukovar, hundreds of Croatians were taken from the city's hospital, bussed to a shed in the country, beaten as they left the bus and later executed. No one says Seselj did any of that. But did he contribute to it? Did his fiery speeches, his calls for a Greater Serbia, his invocations of a past when guerrilla Serbs fought Nazi-supported Croats, influence those who did do it?

A man known as Witness 002 was in the court one May morning to help answer that question. His image on the television screens in the spectators' gallery was pixellated into squares, as if Piet Mondrian were the official court artist. Witness 002 had been a soldier in the Yugoslav National Army in 1991, stationed in and around Vukovar; he had met Seselj there and witnessed the removal of the Croatians from the hospital to the shed, although he said he hadn't seen them killed. Nor had he heard Seselj's alleged cry that not one of the "Ustase" (the wartime Croatian fascist movement) must remain alive.

But for all he didn't see or hear, 002 knew one big thing. "You must understand," he gravely told the court, "that at the time, the laws of Yugoslavia didn't apply." Seselj's own defence - he is defending himself - is a variation on this: that the laws of Yugoslavia at the time were the laws of war, and that, in the context of war, battle cries do not amount to incitements to mass murder. Killing in the context of war, after all, is not usually a prosecutable offence. Milosevic and others arraigned before the Court used the same approach: Yugoslavia had descended into war, and it was each man, each village, each race for itself.

The prosecutors and judges have heard this many times since the Tribunal was established 15 years ago through a resolution by the UN's Security Council. The Tribunal's set end date - 2011 - is now in view, but given the length of the trials (the most famous, of Milosevic, lasted four years and was truncated without a verdict when he died), another two and a half years is not much time to finish the work. Indeed, the arrest of Karadzic almost guarantees a longer run. Fausto Pocar, the Milanese legal scholar who is the Tribunal's president, anticipated this in an interview this spring. Speaking of Karadzic and Ratko Mladic, who is also indicted for crimes of genocide, the mild-mannered Pocar said: "I cannot believe that no one knows where they are. There must be someone who knows - perhaps in the secret services ... It's clearly political."

The Tribunal was the child, in part, of western governments' guilt over doing so little to stop the war in the former Yugoslavia and its related atrocities. But it was also the result of a feeling shared by politicians, NGOs, the media and others that the time had come to assert the principles of human rights - to turn the vaguely termed "international community" into a real constituency, with a real centre of judicial power (the court), that would pursue and punish the worst people on the planet.

The precedent was the trial of Nazi leaders at Nuremberg after the second world war, the first large-scale effort to bring war leaders to book for crimes against humanity. In fact, Nuremberg's creation was beset with concerns about its legality: many, including Winston Churchill, thought it better to dispense summary executions to known Nazis, for fear a trial would both raise sympathy in Germany (it did) and pose legal challenges. Andre Gros, a French member of the commission which set up the trials, argued that, while German aggression in the second world war was an international crime, individual Germans could not be held culpable.

The British member of the commission, Sir David Maxwell Fyfe, took an Anglo-Saxon cleaver to that knot: "We declare what international law is ... there won't be any discussion on whether it is international law or not." Maxwell Fyfe was both right and wrong: the commission did declare what international law was, and acted on it, sending Nazi leaders to their deaths. But it has not ruled out endless discussion on the nature and status of international law: whatever the moral certainty surrounding Nuremberg, its descendants - the ICTY, the International Criminal Court and other tribunals - are continually getting bogged down in ambiguity and rows.

In the case of the ICTY, the most furious of these has swirled around Carla del Ponte, the former Swiss attorney-general who was chief prosecutor from 1999 to 2007. She has become a controversial figure among her former colleagues. John Jones, a British barrister who had been an aide to the Tribunal's first president, Antonio Cassese, says that "Milosevic is del Ponte's biggest failure." Fausto Pocar, the Tribunal's president, says: "I believe the handling of the trials was not done in the best way. Especially that of Milosevic: there were 66 counts against him and so it was bound to take years. Probably it would have been better to have a shorter case, with the likelihood of a faster result." He also criticises her for publishing a book about her experiences at the Tribunal, called La Caccia (The Hunt), in which she criticises her colleagues.

Sir Geoffrey Nice, the chief prosecutor in Milosevic's trial from 1998 to 2001, is more forthright. "She was a disastrous appointment and she did a great deal of damage," he told me. "She had little interest in the details of a case. She was obsessed by publicity." But for all her critics, del Ponte is not responsible for the court's shortcomings. Nice sees the problem as structural: "Domestic courts have governments, democratic parliaments and the media supervising them, and barristers and judges are very vulnerable to making a big mistake, which can ruin their careers. But the UN created this court for political purposes - nothing wrong with that, per se - and then set it loose. That meant that the chief prosecutor of the Tribunal has huge powers: ask any government for anything, make large claims, get publicity around the world."

Nice believes that the judges of the Tribunal have weakened the enterprise, arguing they are "generally not of the top flight". He adds: "Some are industrious and well-respected, truly excellent, as were most of the judges in the long cases I prosecuted, as was the judicial bench in the Milosevic trial. But they are appointed by geographical spread - and some are dumped here; some are academics with little experience; some ex-diplomats with little experience of the law."

Unlike most of the demoralised Nazi leaders at Nuremberg, Milosevic, his health deteriorating throughout his trial, defended himself vigorously and used the occasion to throw back at the increasingly exasperated judges his outraged conviction that he should not be there and that the real criminals were those claiming to be his judges. And for all of the corpses exhumed from cellars, trenches and mass graves, for all of the beatings and rapes and starvation camps recorded and attested, for all the exhortations to cleanse and grab and dominate on his part - the court, at the time of his death, was struggling to pin down the precise nature of his crimes. In an interview that Nice gave to Michael Christofferson, the Dutch director of the documentary Milosevic on Trial, he said: "I shouldn't say this - but it may be better that Milosevic died in the course of the trial. If there had been a judgment, it would have been open to all kinds of challenge, while the record will now remain immensely valuable."

. . .

Vojislav Seselj, like his late president, refuses to acknowledge the court's right to judge him. Unlike Milosevic, however, he appears in rude health; his big belly (it's hard to believe he has recently been on hunger strike) juts out from his jacket as he sits back, staring at Witness 002, following the proceedings with alert interest. He shows his contempt by taunting the prosecutor. At one point, when Seselj is putting his questions to 002, the prosecutor half rises, then sits down again. Seselj roars. "Should I go on? The prosecutor is on his feet - no he's not! There's a problem with his chair! Someone give him another chair!" When the prosecutor complains, on behalf of the translators, that the interchange between Seselj and the witness is too rapid, Seselj says: "The prosecutor hasn't got a problem with me, he's got a problem with himself. He's thinking too slowly. Can I help it if the prosecutor is a slow thinker?"

When a discussion arises about whether the rules of the court follow the Anglo-Saxon model or the continental European one, Seselj interjects: "I do not use anything in my arguments that is not permissible in Anglo-Saxon trials. Remind yourself of what happened in the trial of Oscar Wilde, who also defended himself. I am of course not at his level - maybe 100 per cent higher." And when the judge directs him to stick to the point of his cross-examination, he replies: "I insist on my right to say this is a phoney court with false witnesses. I was not afraid of the bullets in Vukovar and I am not afraid of your judgment."

This bravado travels far beyond the courtroom. On the days Seselj appears in court, two hours of edited highlights of the trial make their way on to Serbian television. In the gallery, fans turn up to cheer his sallies. He remains the leader of the Serb Radical party, for a decade the strongest party in the country. In the presidential elections in May, his deputy and acting party leader only narrowly lost to the current president, Boris Tadic, winning 48 per cent of the votes in a run-off.

In an essay entitled "In Defence of Liberal Show Trials", Mark Osiel, a professor of law and former adviser to the Tribunal, argues that "by highlighting official brutality and public complicity, these trials often make people reassess their fundamental beliefs ... as few events in political life can do". But Milosevic and Seselj have both done the reverse: their trials have confirmed among Serbian audiences the belief that public complicity in official brutality was essential to preserve the Serbian nation from annihilation, whether by the surrounding peoples or by a range of global hostile forces - the sort of forces that have brought these trials and the Court itself into existence.

Seselj sees his nation's history as determined by largely malign foreign powers, especially during the second world war. When the Nazis and Italian fascists invaded Yugoslavia in 1941, a largely Serb guerrilla force fought them, at first in alliance with Tito's communist partisans. Soon, however, they were fighting their former allies as well as the Croatian fascist movement, the Ustase, which ran part of Croatia under German authority. This history deeply colours Serbian nationalists' view of the present. In his trial, Seselj reportedly claimed that a German judge was a Nazi, bent on suppressing Yugoslavia once more. As for Nato, it is seen as the real genocidal force in the world, bent on suppressing independent nations.

For most of the men arraigned at the ITCY, the liberal presumption on which the court is based - that there is a world community willing to stand behind common definitions of criminal behaviour - is nonsense. For them, the world is a mosaic of zero-sum national games in which there are some allies (the staunchest is Russia), but rather more enemies. See, they say, what happens when we challenge our enemies! They drag us before their kangaroo courts to dispense victors' justice!

There is a practical reason why the defendants, not the Tribunal, have captured the public imagination. The trials are often grindingly boring, heavy on detail, challenges, asides, elaborate courtesies. Following an early morning flight, I fell asleep watching the trial of two Macedonians, charged with a murderous attack on the Muslim village of Ljuboten in 2001. I was roused by a stern UN guard, but soon fell asleep again - to be prodded awake by her truncheon. A sole spectator slumbering in the gallery does not enhance the dignity of the court. I claim, in extenuation, some distinguished precedents. Rebecca West, covering Nuremberg for The New Yorker, found the proceedings "insufferably tedious"; and it was "the banality of evil" that famously impressed Hannah Arendt at the trial of Alfred Eichmann.

Guenael Mettraux, a Swiss lawyer who is a defence council in the Macedonians' trial, and edited a remarkable collection of essays on the lessons of Nuremberg, told me that "the press went away after three days of Nuremberg. No one writes about the Rwanda Tribunal ... These are slow and complex affairs." He is a critic of del Ponte and of the court more generally. Speaking to me in one of The Hague's languid cafés, Mettraux says that "Del Ponte would say, 'We need a few Muslims as well as Serbs' - she always wanted the big guys. But the Muslims generally didn't try to commit genocide, or ethnic cleansing. So the cases brought against them tended to collapse." Even the case against Seselj, who is indicted for murder, will be difficult to make, says Mettraux. "There's a big difference between 'what everyone in the street knows' and what you can prove." Seselj has latched on to the controversy over del Ponte's book: he has asked the Tribunal to drop all charges against him, on the grounds that del Ponte writes that the assassinated Serbian prime minister Zoran Djindic had asked her to "take [Seselj] away and do not send him back." This, he claims, contravenes the Tribunal statute's provision which forbids the prosecutor to ask for or receive instructions from any government.

Whether from weariness or because of the deflation of high ideals, the Tribunal professionals seem disillusioned in conversation. Court president Fausto Pocar, noting that the total number of indictments published by the court is 165 (four of which have yet to be served), says with resignation that this represents about 1 per cent of the estimated number of active criminals in the war. Jones, the British former prosecutor - who has co-written the standard work on international criminal practice - says that "initially I was very much a believer: here, for the first time since Nuremberg, was international justice. Then I became cynical - I saw that the judges often didn't know what was happening, the trials were being ruined. And I saw that the UN, which is supposed to supervise, has no moral compass. It enjoins even-handedness, on ethnic grounds, not on grounds of justice."

The ideals are still invoked. In his report to the UN General Assembly last October, Pocar argued that the Tribunal had proved to the world that breaking down the belief in impunity of criminal leaders was possible, and had paved the way for the prosecution of violations of international law in jurisdictions around the globe. Mettraux, asked about the extent of his pessimism, said: "Well, we have shown we can get justice. The idea of international justice is now creeping in, including in the United States - look at their military manuals on the laws of war. What we can do, what we have in part done, is contribute to the sense that there can be some accountability for grave crimes before a world tribunal." Geoffrey Nice is more restrained - but admits that "there is a feeling that there is less impunity than there was. And the verdicts may be useful: they are there, so it will be that bit more difficult for local people to argue that massacres never happened."

Moreover, Milosevic, Seselj and their comrades, indicted or not, lost. Vukovar is a Croatian city; Kosovo is a quasi-independent state; Russia will not "save" Serbia; its new president is a cautious pro-European. The pyrotechnics in court are covering fire for a massive retreat after a war lost.

Yet the larger question remains: has this Tribunal embedded the ideal of global justice into practice? Nearly all those I spoke to, including Pocar, noted that powerful nations against whose leaders a case might be made - Russia, China and the US - would never end up in court. The International Criminal Court, which will continue after the ICTY ends and which was constructed partly on its model, is trying African cases only. And earlier this month, the judge hearing the case against the first defendant, the Congolese Thomas Lubanga - charged with various atrocities, including forcing children as young as 10 to kill - ordered Lubanga's release because of serious legal blunders by, among others, the court's chief prosecutor, Luis Moreno-Ocampo.

On July 14, in a separate trial, Moreno-Ocampo boldly indicted Omar al-Bashir, the president of Sudan, on charges of genocide, crimes against humanity and murder committed in Darfur. Al-Bashir is the first serving head of state to be so indicted (Milosevic had lost power the year before his arrest); and even many of al-Bashir's critics, believe that, whatever guilt he may carry for Darfur, he is crucial to any peace deal. Alex de Waal, a journalist who has covered the issue for the past decade, writes on the website Open Democracy, that, "the prosecutor is striking an immense blow for universal jurisdiction. He is seeking to demonstrate that no one can enjoy impunity for crimes. He is taking a step towards a world constitution in which the barriers of national sovereignty are swept away in favour of the rule of law with global reach." He adds, however, that the issue is not so simple - and quotes a Sudanese political leader, known for publicly supporting the ICC in principle, as saying that this is "a classic case in which justice and stability are at loggerheads". De Waal calls the decision "controversial and fraught with danger", and asks: "Will this be a historic victory for human rights, a principled blow on behalf of the victims of atrocity against the men who orchestrated massacre and destruction? Or will it be a tragedy, a clash between the needs for justice and for peace, which will send Sudan into a vortex of turmoil and bloodshed?"

The question goes to the root of the present ambiguous position of the international courts, poised between what de Waal describes as the "rule of law with global reach" and the deal-making, power-broking, face-saving manoeuvres by which mediating states and institutions induce monsters to stop their horrors. If the rule of international law is to be embedded, it must find a working relationship with realpolitik - while gradually supplanting it. This is a long way from its declarative ideals. With luck, the idealistic step taken will not be taken back. It will need more than luck - it will need substantial political will - for another step forward.

This article has been updated in light of the arrest of Radovan Karadzic.

John Lloyd is a contributing editor to the FT.

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International criminal courts and special tribunals

These courts and tribunals are administered by the UN in partnership with domestic governments.

The International Criminal Court, whose aim is to investigate and prosecute crimes that national courts lack the will or power to pursue, is a permanent tribunal and operates separately from the UN. Its cases are not included here

Former YugoslaviaEstablished May 23 1993The civil war in the former Yugoslavia was characterised by bitter ethnic conflicts, with particularly horrific war crimes committed by Serb and Bosnian Serb forces. The arrest of Radovan Karadzic was announced on Monday. Status: Active, with three arrest warrants outstanding, including that for Bosnian Serb general Ratko MladicStaff: 16 permanent judges and up to nine ad litem judges Budget: $347,566,900 for court proceedings in 2008-09, 18 years will cost approximately $1.5bnNumber of indictments; 161 (as of March 2007)Number of trials completed: 100 (as of March 2007)Number of guilty verdicts: 48 (as of March 2007)Location of court: The Hague, the NetherlandsDistance between court and conflict (in miles): 885

RwandaEstablished November 8 1994Following the assassination of president Juvenal Habyarimana on April 6 1994, the Rwandan army and Hutu ethnic militias murdered more than 800,000, mostly Tutsi, Rwandans. Tharcisse Renzaho, former governor of Kigali, denies charges of genocide. Status: ActiveStaff: 16 permanent judges and up to 18 ad litem judges Budget: $208.4m for 2002-03Number of indictments: 40Location of court: Arusha, TanzaniaDistance between court and conflict (in miles): 425

Sierra LeoneEstablished August 14 2000Founded to prosecute the perpetrators of crimes, including mass rape and amputations, committed during Sierra Leone's brutal civil war. Former Liberian president Charles Taylor denies charges of crimes against humanity.Status: ActiveStaff: Between eight and 11 judgesBudget: $57m over three yearsNumber of indictments: 13 (as of March 2006)Number of trials completed: 6Number of guilty verdicts: 6Location of court: Freetown, Sierra LeoneDistance between court and conflict (in miles): 0

CambodiaEstablished March 17 2003 The UN and the Cambodian government established a joint national and international court to try members of the Khmer Rouge, which killed more than one million people during the 1970s. The Khmer Rouge was led by Pol Pot, who died in 1998.Status: The tribunal started its hearing on February 4 this year.Staff: Six supreme court judges, two additional judges on reserve; plus 30 Cambodian and UN judges for the genocide tribunal for surviving Khmer Rouge leaders in May 2006Budget: $170m for five yearsNumber of indictments: 5Number of trials completed: 0Number of guilty verdicts: 0Location of court: Phnom Penh, CambodiaDistance between court and conflict (in miles): 0

East TimorEstablished July 13 2001Twenty-four years of Indonesian occupation caused the deaths of 102,800 Timorese. Despite a Truth and Reconciliation Commission, the UN's efforts to hold the murderers to account have been largely thwarted by Indonesia.Status: Report published, no prosecutionsStaff: Nine judges, of whom three are Timorese and six internationalBudget: $6.3m in 2002Number of indictments: Almost 400Number of trials completed: 55Number of guilty verdicts: 84Location of court: Dili, East TimorDistance between court and conflict (in miles): 0

IraqEstablished August 11 2005Following the capture of Saddam Hussein on December 13 2003, the dictator and other top Ba'ath party officials were placed on trial. Hussein's execution was on December 30, 2006.Status: ActiveStaff: 14 judges, five trial judges and nine appeals chamber judges, all of whom are IraqiBudget: $138m a yearNumber of indictments: 27Number of trials completed: 7Number of guilty verdicts: 6Location of court: Baghdad, IraqDistance between court and conflict (in miles): 0

LebanonEstablished May 30 2007On February 14 2005 the former Lebanese prime minister Rafik Hariri was one of 24 killed in a car bomb in Beirut. The Special Tribunal was established to try suspects for his assassination.Status: No date setStaff: Three judges - including veterans of the tribunals for Rwanda and the former Yugoslavia Budget: $120m over three years, $35m for its first year (2008)Number of indictments: 0 (trial has yet to begin)Number of trials completed: 0Number of guilty verdicts: 0Location of court: The Hague, the NetherlandsDistance between court and conflict (in miles): 1,990