Prosecutors in the German city of Stuttgart have confirmed they are investigating a former Nazi SS man for crimes at the Auschwitz death camp.
Hans Lipschis, 93, worked at the camp in German-occupied Poland from 1941 - he says as a cook, German media report.
His name appears as number four on the Simon Wiesenthal Center's list of most-wanted Nazis.
German media have identified him as living in Aalen in southern Germany. He has not yet been charged.
Lipschis is among 50 former Auschwitz staff, still alive, who are being newly investigated by the German authorities.
Auschwitz was the biggest Nazi death camp, where more than 1.1 million people, most of them Jews, were murdered.
Prosecutors point to a re-interpretation of criminal law after the conviction of John Demjanjuk, in May 2011.
Demjanjuk was found guilty of being an accessory to the murder of 28,060 Jews while he was a guard at the Sobibor death camp in occupied Poland.
His case means that potential defendants such as Hans Lipschis might no longer be able to hide behind the argument, in court, that they were simply following orders.
Sense of justice
"Simply being where the killing took place would be enough for a conviction," according to Kurt Schrimm, head of Germany's Central Judicial Office for the Investigation of Nazi crimes.
He says the purpose of pursuing suspects now is to create a sense that justice is being done and to shed light on historical events.
"We owe it to the survivors not simply to say that a certain time has passed and that it should be swept under the carpet," he says.
Hans Lipschis' wartime identification papers prove he belonged to an SS-company deployed as guards in Auschwitz.
It is not clear what role, if any, he had in the mass murder of inmates. He has told neighbours and reporters he worked only as a cook and saw nothing of the gas chambers and crematoria.
One German newspaper says Lipschis, who was born in what is now Lithuania in 1919, finished World War II fighting for Germany on the eastern front.
He moved to Chicago in the US in 1956, where he lived until 1983, when he was expelled for having concealed his Nazi past.
Accessory to murder
At the time it could not be proved that he was personally responsible for any killings.
He returned to Germany and his whereabouts, in Aalen, has apparently always been known to the authorities.
He may now be charged with being an accessory to murder.
It is not yet clear if and when his case will come to trial.