Scotland Yard has interviewed more than a dozen witnesses, in several countries, who back a case suggesting the man led a battalion that killed civilians in what is now Belarus.
The Polish-born suspect, now a British citizen, has lived in a semi-detached house in a commuter town for more than 20 years, with his wife and son. He is alleged to have helped into Britain at least 20 other men suspected of war crimes.
The battalion was allegedly recruited by the Germans to carry out out Hitler's liquidation policy against civilians, mainly Jews, around the town of Mir, near Minsk. It is claimed that when the battalion began operating in 1941 more than 4,000 Jews livedin the area. Four years later only 30 remained.
Witnesses in Belarus have made statements and the case is understood to be supported by military records.