Jasenovac concentration camp complex, on the bank of the Sava river, was the largest extermination centre in the wartime Croatian Nazi-puppet state, known as the Ustashe regime (NDH).
Mr Sakic, 76, was extradited from Argentina in July 1998, where he had been living since 1947 with his wife Nada, a former guard at the nearby Stara Gradiska camp. She was also extradited from Argentina to stand trial for her wartime activities, but has since been freed.
Some 600,000 people were killed at Jasenovac, according to the Encyclopaedia of the Holocaust, mostly Serbs, but also Jews, gypsies and opponents of the Ustashe regime. Like every question of history in the Balkans, the number of victims of Jasenovac is the subject of furious debate. Croatian historians, keen to downplay the number for political reasons, put the figure at around 35,000, and the actual total will probably never be known.
Croatian officials launched a criminal investigation into Mr Sakic after he gave an interview in April 1998 to Argentine television in which he was said to have acknowledged that he was a commander at Jasenovac.
Unlike Auschwitz or Belsen, Jasenovac is not a well-known name outside the former Yugoslavia. A memorial still stands there, although the Tito- era museum was destroyed during the Croatian war of independence.But survivors and historians have chronicled its history of appalling brutality.
There were no gas chambers at the Jasenovac complex, because they were not needed to carry out mass murder. Instead, the guards slaughtered inmates by hand, favouring knives and hammers, as well as bullets. Under the watchful eye of guards such as the former Catholic priest, Miroslav Filipovoc- Majstorovic, guards would hold competitions to see who could kill the most prisoners.
The corpses were then thrown into the river Sava, which ran red with blood. Such was the Ustashe guards' brutality that even SS troops at Jasenovac were disgusted, and wrote protesting memos to Berlin.
On television Mr Sakic denied that he had been involved in brutality. "Nothing happened in Jasenovac," he said. "It was a work camp where the Jews managed themselves. We never put a hand on any of the prisoners in the camp. The people died of natural death. There was a typhus epidemic for example, but there were no cremation ovens that killed anybody."
Both Croatian officials and Jewish organisations had probably known for years of Mr Sakic's whereabouts in South America but it took the interview to nudge them into action. Afterwards a Zagreb district court judge, Miroslav Sumanovic, called for his arrest, "because there are suspicions that he committed the gravest and most fatal form of criminal act, punishable in law by the maximum penalty".
The Croatian government, ever-keen to show its Western, rather than Balkan credentials, has worked closely with both the US State Department and Jewish organisations, such as the Simon Weisenthal Centre in Los Angeles, in the Sakic case.
The trial could be a turning point in the history of this former Yugoslav republic, independent since its birth in blood and fire in the summer of 1991, as it comes to terms with its predecessor, the NDH. The young state has for years been dogged by accusations that it draws inspiration from the NDH and the Ustashe. The current Croatian national symbol, a block of red and white squares, is almost identical to that of the NDH's emblem. The "U" symbol, for the Ustashe regime, can be seen sprayed on walls.
The controversy over Croatia's wartime past reaches as far as the presidential palace. In his book The Wastelands of History, President Franjo Tudjman, a former anti-Nazi partisan, appeared to downplay the Holocaust and the number of Jews killed. Israel refused to establish full diplomatic relations with Croatia until he apologised for his writings.
The trial is also likely to prove an embarrassment for the Vatican, if Mr Sakic chooses to reveal details of how papal officials aided former NDH leaders, such President Ante Pavelic, fleeing to South America. Many Ustashe killers fled the advance of Tito's partisans along the notorious "rat-lines", the underground escape routes for officials of the devoutly Catholic Ustashe regime, where Croatian fascists were provided with funds and passports by Catholic priests as they passed through Italy.Reuse content