He was named publicly as a suspected war criminal in 1986. Until then the Jewish family in the neighbouring terrace house, and his Sri Lankan-born wife, knew nothing of his wartime experiences.
Last week, in the wake of the release of Demjanjuk, who had been sentenced to death for the war crimes of another man, the Nazi-hunting Simon Wiesenthal Centre in Israel issued a list of the 15 most-wanted war criminals. At the top was Alois Brunner, a German who was Adolf Eichmann's right-hand man and was last interviewed in Syria, when he proudly defended his war record. Second was Mr Gecas, originally from Lithuania.
Antanas Gecevicius, as he was called before he came to Britain, commanded a platoon in the 12th Lithuanian Auxiliary Police Battalion, a squad used by the German army to round up Jews in its territories and murder them.
Greville Janner, the Labour MP, named Gecas under parliamentary privilege as a man on the list of suspects in Britain supplied to the Home Office by the Wiesenthal centre. At that stage there was no question of prosecution, because neither English nor Scottish law covered crimes committed abroad by foreign nationals, even if they subsequently became naturalised British.
The 1991 War Crimes Act made it possible to launch a prosecution and a unit was set up in London to co-ordinate investigations. Scottish law is different, but the evidence against Gecas was so strong that a separate unit was set up in Edinburgh to prepare a case against him. The unit of researchers and officers from Lothian police have spent an estimated pounds 600,000 travelling the world collecting evidence.
Mr Gecas is a sturdy, grey- haired man with a slight stoop. His life divides into three, each apparently in a watertight compartment in his mind.
In compartment one, from his birth in 1916 up to the outbreak of war in 1939, he was a middle-class schoolboy and became a successful Lithuanian air force cadet. The second Mr Gecas, one he now denies existed, came into being during the war. In 1941 the Germans annexed Lithuania in their sweep into the Soviet Union.
The young Gecas joined a Lithuanian police battalion as a lieutenant in charge of a platoon. The battalion killed thousands of Lithuanian Jews taken from city ghettos and from small towns and villages to be shot. By autumn 1941, when few Jews were left in Lithuania, the battalion and others were taken by the Germans to do a similar job in German-occupied Byelorussia (now Belarus).
By 1944 the battalion was being used to help bar the Allied advance through Italy, and in September Mr Gecas's company was captured by the US army.
He changed sides and fought for a Polish regiment, and after the war was able to launder his past and come to Britain as a Pole. By 1956 he was a full British citizen. He married in 1959 when he was 43 and his wife a 19-year- old nurse. He worked for the National Coal Board until his retirement in 1981.
The discredited identification evidence against Demjanjuk was from surviving victims. Mr Gecas, were his case to come to court, would have to discredit the testimony of several officers who served alongside him for months or years. He has accepted publicly that he joined the battalion, went with the Germans to Byelorussia, and later wore German uniform and fought in Italy, but says if Jews were rounded up and killed he had no knowledge of it. He claims to have no recollection of ghettos even existing.
Mr Gecas has avoided any comment since a libel action he brought against Scottish Television failed. Months ago the Scottish police team completed its dossier on the Gecas case, and to all intents and purposes was wound up. For some reason the Advocate General, who in Scotland decides whether it is in the public interest for a case to proceed, has so far failed to say what his decision is.