A cup of coffee and a quiet chat about unimaginable evil

In the waiting room of the UN's International War Crimes Tribunal in The Hague, a young woman tells me that Judge Goldstone will see me at 4pm sharp. She offers me coffee and a pamphlet on how to dig for mass graves. "I think you'll find this interesting," she says.

The tribunal's Bulletin No 8 is printed on green paper and adorned with a photograph of a skeleton draped in tattered clothes. "Forensic experts use high-tech equipment, such as electronic mapping procedures, to measure and map precisely the entire grave area, artefacts, human remains and other objects," the article tells me. "The team searches for bodies by using a two-metre T-bar shaped steel probe, which is plunged into the ground and smelled for the odour of decayed remains." The smell of freshly brewed coffee drifts from a little office by the door.

"The position of the bodies can be a key to establishing how the victims were killed ... whether victims were lined up and shot, and from what angle, and whether they were bulldozed into the site after being executed."

By the time I am ushered in to meet Judge Richard Goldstone, I am ready to discuss the nature of evil with the chief prosecutor of the first war crimes tribunal since the Nuremberg trials. The dapper South African who greets me in shirtsleeves, however, expects to be asked about the law. I want to know how men can produce - in the words of the UN indictment of the Serb war criminals Radovan Karadzic and Ratko Mladic - "scenes from hell, written on the darkest pages of human history". But Mr Goldstone is an unemotional man. Even the mention of Srebrenica, a place in whose name the tribunal has accused Karadzic and Mladic of the slaughter of up to 8,000 Muslims, produces a reply that is as legalistic as it is clinical.

Did not Dutch troops stand by while dreadful deeds were done? "The Dutch were in a hopeless and helpless position," he says. "But here's the analogy I use - the feelings I would have if I am going past a raging river and see a young child of two or three drowning. I know that if I jump in and try to save the child, I'm going to drown too. And I walk away. If I know absolutely - with an absolute certainty - that I would have drowned too, I'm going to have sleepless nights. But there is no point in some suicidal gesture. And that's the position the Dutch battalion were in. They asked for reinforcements. They didn't come.

"The people who make these policies" - and here Mr Goldstone was taking aim at senior UN officials - "don't take into account the victims. What could be more unfair than sending armed, uniformed people to give protection - and tell them that their instructions are not to give protection?"

This response is troubling, for two reasons. Firstly, no one can be certain a rescue attempt will fail - which may be why he twice used the word "absolutely" - and, secondly, the little girl would have to have been thrown into the river to make the analogy applicable to the bloodbath at Srebrenica, which was an atrocity, not a tragedy. So I return to the question of evil. What creates the dividing line, I ask him, between a law-abiding man or woman and a human being who is wicked?

There is a long silence from the man who has listened for more than two years - again to quote his tribunal - to "evidence ... of unimaginable savagery: Thousands of men executed and buried in mass graves, hundreds buried alive, men and women mutilated and slaughtered, children killed before their mothers' eyes, a grandfather forced to eat the liver of his own grandson ..."

Mr Goldstone's eyes flicker ever so slightly. "I don't think any human being is wholly bad or wholly good. It's like a threshold of pain. No two people have exactly the same threshold. So where anybody is going to slip over from being a law-abiding citizen to become a rapist or a murderer is a very subjective thing. It's like experimenting with rats. Some rats learn very quickly how to get to the cheese, others take longer. I don't think human beings are any less animals. We're more sophisticated and complex, but we are all of the same species. It's a matter of degree."

If Mr Goldstone seems a passionless man, he is also a man of courage and high moral principle. Under constant death threats he chaired South Africa's 1991 commission into the causes of violence, accusing the highest police officers of using a convicted murderer as part of a "dirty tricks" squad to destabilise the country's emerging democracy.

Witwatersrand University in Johannesburg provided his first experience of injustice. "It was the first time I had met black South Africans as peers. We were equals. But the minute my black friends walked out of the front entrance of the university, we were treated completely differently. They had to carry passes. I didn't. They had to go back to segregated townships. Many had no electricity and had to study by candlelight. I went home to a middle class suburb and had a comfortable study and a good reading lamp ... This wastremendous injustice. It got meinvolved in student politics."

As chief prosecutor for the UN War Crimes Tribunal in Rwanda, he listened to evidence of epic slaughter - "I have my nightmares before I go to sleep," he mutters. This genocide appears to have shocked him even more than Bosnia. "Literally, it was neighbour against neighbour and in many cases spouse against spouse, murdering each other because of indoctrination and unbelievable organisation. It's really almost unbelievable that some 850,000 people could be killed in three months. That's an amazing fact. And it could only be done because it was well organised."

So why are we now bothering to prosecute war criminals in Bosnia? Was not the 1982 Syrian slaughter of 20,000 civilians at Hama a war crime? Was not last April's Israeli massacre of 105 civilians under the UN's protection at Qana in southern Lebanon a war crime? What about Saddam Hussein's gassing of Kurdish civilians at Halabja? Judge Goldstone makes no mention of Hama and Qana, but he accepts that Halabja - along with the Cambodian genocide and the killing of civilians in Somalia - were war crimes. So why not hold a war crimes tribunal into the 1915 Armenian holocaust, when 1.5 million Christians were massacred and their women raped - as a matter of policy, just as in Bosnia - by Turks and Kurds?

Mr Goldstone reminds me of Hitler's reported remark to the German foreign minister, Joachim von Ribbentrop, in relation to the Jews - "Who now remembers the Armenians?" - and bluntly acknowledges that the Armenians will not receive justice. "They've missed it. The boat didn't come into their harbour." That is a harsh judgment, but the judge is a man who must deal with hard facts.

"They were entitled to justice. It wasn't offered to them by the international community. But standards and morality have changed. I think there's more recognition today of the unacceptability of this sort of conduct. I think the law of war has advanced. These tribunals have for the first time made people aware that there is such a thing as international humanitarian law."

But is that really true? Mr Goldstone's court has issued 74 indictments - most of them against Serbs - and yet only seven men have been arrested for their crimes in Bosnia, a pathetic figure and an indictment against Nato and its Western leaders, who do not want to risk their soldiers' lives. Karadzic remains at large, while Mladic sits in his nuclear bunker in the French brigade's sector of Bosnia.

Mr Goldstone has strong views on the subject. "If there was in England some serial murderer who's a wanted man, no commissioner of police is going to make a public statement saying: 'Well, you know, this chap's too dangerous - I'm not going to put my policemen's lives at risk.' The purpose of justice is to officially acknowledge to the victims what happened to them. In a domestic rape, because you know who raped your daughter, you still want him put on public trial and punished. You want society to officially acknowledge what happened to you."

So what chance that we would see Messrs Karadzic and Mladic at The Hague after Mr Goldstone retired from the court, which he does tomorrow? His reply was political rather than legal, even a trifle cynical. "Bosnia and Croatia and Serbia are very anxious to become part of Europe. They're not going to if they don't accept their international obligations [to hand over indicted war criminals]. People who are in office have a great deal of importance. But when you lose office, that charisma - that importance - disappears very quickly. And former leaders are much more expendable than people in office."

Serb warlords betrayed by their former underlings? It seems too good to be true. I ask Judge Goldstone to sit at his desk for a photograph and, through the camera lens, I notice how relaxed he seems, how easily he folds his hands and gazes out of his window at the rain sluicing down.

"I think you are a very self-confident man," I say. And he looks up sharply, unsmiling, staring into the camera. "Am I?" he asks.