The only man to have been convicted in Britain of Nazi war crimes has died in Norwich Prison.
Sawoniuk moved to the UK in 1946
Anthony Sawoniuk, 84, was serving two life sentences after being found guilty of murdering 18 Jews in the UK's first war crimes trial.
The former British Rail ticket collector was found guilty in 1999 of crimes committed in his home town of Domachevo, Belarus.
He lost an appeal against his conviction in 2000.
Police said Sawoniuk was believed to have died of natural causes and his death was not being treated as suspicious.
He was tried at the Old Bailey, London, and jailed for his role in the Nazi genocide in eastern Europe after more than 50 years at liberty.
Sawoniuk, who moved to the UK after the war, sealed his own fate with a letter written in the early 1950s to his half-brother Mikolai in Poland.
At the time, all mail from the West was vetted by the KGB, which already had Sawoniuk on its records of possible war criminals who had escaped abroad.
As the Soviet Union began to break down in the mid-1980s the list was submitted to British authorities.
However, Sawoniuk's name had been spelled wrong. Only in 1993, when the names were reviewed, did it emerge that one of the men on the KGB records had moved to Britain.
By the 1990s Sawoniuk had retired after an unremarkable routine of 25 years working as a ticket collector for British Rail, and living in Bermondsey, south London.
He had slipped into the UK under the guise of a Polish patriot after switching sides late on in the conflict.
Sawoniuk was born on 7 March 1921, in the harsh climate of Domachevo. As a boy he would have starved if it were not for the generosity of local wealthy Jewish families.
But when the Germans arrived in 1941, he took up with the Nazi police force to help with the suppression and genocide of local Jews.
During his trial, the jury heard from an eyewitness how he watched Sawoniuk tell two men and a woman to strip beside an open grave and then shot them.
The court also heard how he mowed down 15 people with a submachine gun and pushed their bodies into an open grave.
The jury travelled to Belarus to visit the scenes during the trial.
In February 2005 Sawoniuk was transferred to Norwich Prison from Kingston Jail in Portsmouth and was held in a unit for elderly life prisoners.
A police spokeswoman said a normal coroner's inquiry would now take place.