An 84-year-old Nazi war criminal serving two life sentences for the murder of 18 Jews has died in a British jail, authorities said Monday. Anthony Sawoniuk, the only person to be convicted of Nazi war crimes in a British court, died in Norwich Prison, in eastern England, on Sunday, a Home Office spokeswoman said. The death was attributed to natural causes. Sawoniuk had been suffering from a terminal illness and police said his death was not being treated as suspicious. Sawoniuk - originally from Domachevo, Belarus - moved to south London in 1946 where he worked as a railway ticket collector. During a war crimes trial in Britain in 1999 Sawoniuk pleaded innocent to involvement in Nazi genocide in Eastern Europe more than 50 years earlier, but witnesses implicated him in a series of murders. He was found guilty of two charges of murdering Jews in his hometown of Domachevo in 1942 while serving in the local Nazi-backed police force. John Nutting, the prosecutor in the Sawoniuk's trial at London's Old Bailey court in 1999, said Sawoniuk was "not only prepared to do the Nazi's bidding, but carried out their genocidal policy with enthusiasm." The trial was told Sawoniuk gunned down two Jewish men and woman and also ordered 15 Jewish women to strip and face an open grave before killing them with a machine gun. Sawoniuk later served with the Waffen SS, but when he saw the Germans were losing the war he changed sides, joining the Polish army and fighting with the allies. Posing as a Polish patriot, he emigrated to Britain in 1946. His past was uncovered after a letter to his brother in Poland was intercepted by the KGB in 1951. But he wasn't pursued until KGB files were transferred to Britain after the fall of Communism. Then it took police, historians and linguists months to track him down. Police said a coroner's inquiry would be opened into Sawoniuk's death and the Home Office spokeswoman said a prison ombudsman would also investigate the death. "That's what happens to all deaths in custody, just to make sure everything operated smoothly," she said.