He is in Hong Kong this week to speak in Asia for the first time about his painstaking work. Last night, he spoke at the Jewish Community Centre at a ceremony to commemorate UN International Holocaust Remembrance Day, which is today.

He said he aims to raise awareness about the genocide and mass murder hoping to prevent these atrocities from happening again.

'For me, genocide is a disease of humanity,' he said. 'If you do not recognise a disease you cannot treat it.'

The goal of Desbois' organisation, Yahad-In Unum, is to uncover all mass graves in Eastern Europe, and collecting witnesses' testimony is key. The group has filmed 1,760 witnesses testifying about the shooting of Jews and Roma.

'When I began, people told me: 'It's impossible what you do, Father, because it was a secret. There were no witnesses',' Desbois said. But, he said: 'I'm sorry, there are witnesses everywhere.'

Desbois said some witnesses had been relieved to finally tell stories which had haunted them for nearly a lifetime.

One witness, who was a non-Jewish teenager during the war, said she was forced to walk barefoot on the corpses to compress them into mass graves. She never told anyone about this.

'And she told me: 'Suddenly all my schoolmates arrived because they were Jews, and I had to walk on them like the others',' he said.

Time is against Desbois and his team, who must trawl through German and Soviet archives, visit remote villages to interview witnesses and complete research.

'We want to finish before the witnesses die,' he said. 'It's a short-term challenge. The witnesses are between 75 and 90. They were teenagers during the war, and they want to speak before they die.'

In Hong Kong yesterday, he admitted being apprehensive about whether his findings would be meaningful to an Asian audience. But after the first few days of lecturing students, his fears have subsided. Their sensitive reactions and insightful questions have been a welcome surprise. 'It gives me great hope to arrive in Hong Kong and find teenagers who are concerned,' he said.

He said genocide has occurred unexpectedly at many times and places.

The Germans were highly educated and cultured, their genocide of the Jews 'unthinkable', Desbois said.

Rwanda's genocide in 1994 was just as unexpected. 'Everybody was Catholic, both sides had the same religion, same condition, all blacks. Who could imagine a tribe could absolutely try to exterminate another tribe?'

The 1937 mass murder in Nanking by the Japanese against the Chinese is an event that Desbois has used as a reference during his talks to students.

'It was nearly the same methodology used by the Japanese in Nanking that was used by the Nazis in the Soviet Union: to shoot everybody,' he said.