It was dramatic. He was defiant. It was live. This was judicial theatre at its best. The man the tabloids had once called the Boss of the Balkans had now been redubbed the Butcher of Belgrade. He was in the dock and he was snarling.

"I consider this tribunal a false tribunal and the indictments false indictments." The words, in English, were those of Slobodan Milosevic. He was playing, not to the court, but to the widest possible audience beyond the court, those watching live around the world. The indictment he considers false runs to 32 pages and accuses him of war crimes and crimes against humanity in ordering the murder of hundreds and the deportation of hundreds of thousands of Kosovo Albanians before and during the NATO bombing of Serbia in 1999. The British chief judge, Richard May, asked Milosevic if he wanted the indictment read out in court.

"That's your problem," Milosevic said. He refused to enter a plea. He had refused to hire lawyers. The court entered a not-guilty plea for him. Then he was sent back to his isolation cell in the Sheveningen prison. As he left the courtroom he tapped his watch and said, again in English, "fifteen minutes." That's all, he seemed to be suggesting, the court would give him in public before locking him up for another two months. When he had started speaking in Serbian, saying the real war crime was the NATO bombing of Serbia, the chief judge had cut him off. It wasn't the time for speeches, Richard May said.

There was an evident sense of triumph at the tribunal the day after Milosevic was flown in from Serbia. The president and the chief prosecutor talked of the dawning of a new era. It was hardly an exaggeration.

Just a day after Milosevic was arraigned, the prime minister of Republika Srpska, Mladen Ivanic, showed up for talks with the chief prosecutor, Carla Del Ponte. He came bearing a gift: the promise of a law on co-operation with the tribunal to be passed soon by the parliament of his rump republic in Bosnia. The gesture was important because Republika Srpska harbours two of the world's most notorious fugitives: Radovan Karadzic and Ratko Mladic. During the murderous Bosnian civil war they were the political and military leaders of the Bosnian Serbs. Their brutal militia was responsible for some of the worst atrocities of the conflict, including the mass killings at the enclave of Srebrenica in 1995. Both men are under indictment for war crimes and crimes against humanity.

Ivanic quickly found that his gift wasn't enough. At a news conference after their talks, Del Ponte rounded on him. "At any given time the authorities of the Republic of Srpska know or are in a position to know the whereabouts of our most wanted fugitives. Ratko Mladic has been enjoying the protection of the Bosnian Serb forces. This unacceptable situation must come to an end now." Ivanic could only mutter that he didn't think his police and army were protecting the men but he would check.

Three days later Croatia announced it would turn over two senior generals indicted for war crimes by the tribunal. It was a controversial decision and brought about the resignations of several ministers but it demonstrated the suddenly increased clout of the tribunal.

Bringing in the big fish has been hard enough; trying them will be another major test for The Hague tribunal. Milosevic's snarling entrance into the judicial arena is only the first round. Geoffrey Robertson is an English lawyer and an expert on international human rights law. He says the trial of Milosevic will be, in effect, the trial of the tribunal. The former Yugoslav leader has already signalled he will challenge the court's jurisdiction. This, according to Robertson, is the Charles I defence. Charles I is the only king of England to be beheaded. It happened after the English civil war in 1649 and after a trial in front of the British Parliament.

"Charles refused to defend himself. He was executed but it raised questions forever after about the case," Robertson says. "He transformed himself from a brutal butcher to a martyr in the eyes of history. Hermann Goering, the Nazi Reichsmarshal, tried to do the same thing at the beginning of the Nuremberg trials. He got all the top Nazis in the dock together and read them a quote from Goethe, which roughly translated, says 'kiss my ass.' And, he said, that's what we should say to the court. And that's what they did for the first few months. But then the justice game got the better of them. They realized they were going to get a fairish trial. They realized it was their last chance to explain themselves, to lessen the blackness that was descending on their names. And at the end they fully co-operated with the court.

"The longer the process goes on at The Hague for Milosevic, and we're talking about five years because there'll be a second trial with a genocide indictment for presumed crimes in Bosnia, the more the temptation for him will be to put, not the court on trial, but NATO on trial. He's got a choice. If he just sits in his cell for five years, he'll miss his chance of claiming it's all NATO's fault."

And Robertson believes Milosevic could make a plausible case. "On one view of international law, a view of many legal scholars, NATO's action in Kosovo and Serbia in 1999, its bombing campaign, an action without UN approval, was an incursion into sovereign space and was unlawful. If Milosevic wants to make that argument [he could] say, well, I was justified in deporting 740,000 Albanians because they were potential fifth columnists once NATO started bombing. He could make that argument if only he comes to court."

He could also, Robertson believes, make the embarrassing argument that the chief judge on the case is from a NATO country. Judge Richard May is British. "The tribunal must be seen to be fair. At the end of the day, if international criminal justice is to be successful, this trial must be successful. And by successful, I don't mean convicting him necessarily. Acquitting him if there is a reasonable doubt." And the problem will be, not to prove that crimes took place, but to link them to orders from Milosevic.

Whatever the outcome and however long it takes, it will be, Robertson believes, "the trial of the 21st century."