The fireman's hall on Primorska Street, a crimson and white building with a large Croatian flag, is a centre of Pozega's community life, rented out for wedding parties and operettas.

On Christmas Day 64 years ago the hall was not a place to party. Around 150 of this country town's Jews were rounded up, penned here, robbed of their valuables, and put on cattle wagons bound for the concentration camps of fascist Croatia's Ustasha state. They all perished, along with hundreds of other local Jews and Serbs. By 1942 the town's entire Jewish community, the oldest in the central and eastern part of Croatia called Slavonia, were wiped out.

The police chief in what was then a small town of 7,000 was a young Zagreb-trained lawyer called Milivoj Asner. Now 92 and living in the southern Austrian city of Klagenfurt, Mr Asner both denies and indirectly confirms his role in the pogroms. "I was just the town police chief, dealing with traffic offences, petty crime, thievery," he told the Guardian. "I did not hate Jews as such. I have many Jewish friends."

But for Efraim Zuroff, the Israeli-American Nazi-hunter who has inherited the mission of the late Simon Wiesenthal, the Asner case is at the centre of his Operation Last Chance - his campaign, mainly in eastern and southern post-communist Europe, to bring ageing war crimes suspects to justice before they die. "As Simon would say," said Mr Zuroff, "he who ignores the murderers of the past paves the way for the murderers of the future. But it's very difficult in eastern Europe for these post-communist societies to face up to their complicity in genocide."

As head of the Jerusalem-based Simon Wiesenthal Centre, Mr Zuroff is trailing dozens of Nazi suspects from Estonia to Romania to Australia. The copious documents unearthed by a young Croatian amateur historian on the Asner case, said Mr Zuroff, makes this case the most promising of more than 80 he has forwarded to authorities in nine countries. "This case is highly important," he said. "It's fully documented. There's an extradition request, there's an arrest warrant. It's the nearest we've got to a trial."

After heading Pozega's police in 1941-42 Mr Asner disappeared amid the chaos of the early post-war years, fleeing Croatia, where the victorious communist authorities quickly named him as a war criminal, to Austria where he obtained Austrian citizenship.

And that was that for the next 50 years until Alen Budaj, then a 19-year-old amateur historian from Pozega, started researching the fate of the town's Jewish community and obtained documents allegedly incriminating the former police chief. He discovered Mr Asner had been living prosperously in Austria since 1945, but had returned to his hometown, Daruvar, near Pozega, in the early 90s when the extreme nationalist President Franjo Tudjman was in power. Mr Asner felt welcome.