Harry Svikeris, 83, suffered a heart attack and was found dead at his home in Milton Keynes, Buckinghamshire, 10 days ago.
He was an officer in a collaborationist Latvian paramilitary police unit which rounded up and shot thousands of Jews and other civilians after the Germans invaded Latvia. Mr Svikeris, who had taken British nationality, moved to Milton Keynes from Wales 13 years ago, and is said by sources close to the investigation to have been for a long time a strong candidate to be the first man prosecuted under Britain's 1991 War Crimes Act.
His widow, Alice, said: "I don't know anything about what he did in the war. He is dead ... I have his ashes upstairs, don't blacken his name, leave him in peace."
Neighbours said they had no idea of his past, or that the police were investigating him. They said he seldom left the house. His married daughter lives near by.
Last month, police charged Szymon Serafinowicz, 84, born in Belarus and now living in Banstead, Surrey, with four counts of murder under the War Crimes Act. He is accused of killings in Belarus in 1941 and 1942, and was remanded on conditional bail by Epsom magistrates until 5 October.
Mr Svikeris's file was one of six others sent to the Crown Prosecution Service for a decision last year. CPS lawyers recommended four cases should be dropped, and Mr Svikeris and one other case needed further investigation. Days before he died, Mr Svikeris had been told he was not being charged - for the time being.
The auxiliary police unit he served in was formed in July 1941 under the leadership of Victor Arajs. Its only purpose, according to Eli Rosenbaum, director of the Office of Special Investigations in Washington, was to kill all the Jews in Latvia.
The Arajs Kommando was used by a German Einsatzgruppen, one of the mobile killing squads who carried out Hitler's final solution.
Documents in the police files, which are several thousand pages long, show the Arajs Kommando had 500 men.
The Germans kept meticulous records and applications for weapons permits show that Mr Svikeris was an officer from at least November 1942, and that in March 1942 he was in charge of the 1st and 2nd companies of the Arajs Kommando.
It is alleged that during this period these companies burnt down the villages of Sanniki and Malinova, shooting all 300 inhabitants in the process.
As the Russians began to re-occupy the territories later in the war, the Arajs Kommando was recruited to fight for the Germans. Mr Svikeris was allowed into Britain in 1947 or 1948 from British-occupied territory in Germany where his unit had surrendered. He was part of a programme to recruit useful workers for British industry and agriculture.
He was first questioned seven years ago when a commission under a former Director of Public Prosecutions,Sir Thomas Hetherington, was establishing whether there were sufficient cases in Britain to justify changing the law to allow for their prosecution.
Sir Thomas's confidential report said that Mr Svikeris did not deny being in the Arajs Kommando, but more evidence was needed to demonstrate that he ordered specific massacres.
The OSI, America's war crimes unit, has investigated other members of the Arajs Kommando who emigrated to the US. One, Konrads Kalejs, was deported to Australia, where he had first taken citizenship after leaving Europe. Another, member of the unit, Mikelis Kirsteins, of New York, had a heart attack soon after his case was filed.
Arajs himself was sentenced to life imprisonment for mass murder in Germany, and died in jail in 1988. Scotland Yard's war crimes unit is working on 14 other cases.Reuse content