Anton Gecas, 76, a retired mining engineer who came to Britain as a refugee in 1948, has been the subject of a Scottish police investigation since the War Crimes Act was passed in 1990, extending jurisdiction for murder to men who were not British at the time the crimes were committed. During the Second World War, he was an officer in a Lithuanian 'police' battalion set up under the Nazi occupation.
The Scottish police team - a small unit under Lothian and Borders force, based in Edinburgh - has completed its case against Mr Gecas, but is relying on 13 former members of his old platoon now living in London and Yorkshire. The Scots believe these 13 men should be given immunity from prosecution.
However, the Scotland Yard War Crimes Unit, which is responsible for investigating suspects living in the rest of Britain, wants to retain the right to prosecute these men as well.
Mr Gecas was found to have committed war crimes by a Scottish civil court earlier this year, after he had sued Scottish Television over a documentary about him in 1987. The issue came to a head this week, because until Thursday it was still possible that Mr Gecas would appeal against the verdict of the libel trial. He did not and is now out of time.
The issue will be discussed at a meeting in London next Thursday of the two forces, together with representatives of the English Crown Prosecution Service, and the Scottish Crown Office.
The Scots are expected to argue that unless they are granted immunity, the 13 witnesses will say they cannot remember in any detail events which took place 50 years ago, and that their crimes were less heinous, because they were privates while Mr Gecas was a lieutenant.
Before and during the libel trial there had been doubts over the reliability of elderly Lithuanian witnesses, some in poor health, who had diluted their allegations against Mr Gecas since making them on camera in 1987, before Lithuanian independence. He had claimed the evidence was a conspiracy against him, the result of KGB pressure on witnesses.
But the trial judge, Lord Milligan, found the case against Mr Gecas overwhelmingly proved. In his judgment, delivered in Edinburgh on 17 July after a long libel trial including evidence from witnesses in Lithuania, Lord Milligan said he was 'clearly satisfied' that Mr Gecas had 'participated in many operations involving killing of innocent Soviet citizens, including Jews, in particular in Belarus during the last three months of 1941, and had committed in addition war crimes against Soviet citizens including old men, women and children'.
He also found it proved 'Gecas was platoon commander of the 12 Auxiliary Police Battalion and that the platoon participated specifically in six operations. It inevitably follows that (Gecas) committed war crimes against innocent civilians of all ages and both sexes in the course of those operations'.
Mr Gecas accepted that he joined the battalion in 1941, stayed with it as a lieutenant when it went with the Germans to Belarus, then after 1943 wore a German uniform and went to fight in Italy. (Later he switched sides along with the rest of his platoon and joined Free Polish forces fighting for the Allies, and was decorated for bravery. Many of his comrades later settled in Britain.)
But if Jews were rounded up and killed in tens of thousands by Lithuanians, as historians and contemporary documents produced in court said, Mr Gecas said he had no knowledge. If his battalion took part in killings, he maintained, his platoon was always elsewhere at the time.