She looks like someone’s harmless grandmother waiting for the man to come to read the meter or repair the boiler. But this little old lady is one with a dark past and a unique claim to infamy.

For Frau Erna Wallisch, 85, ranks number seven on the Simon Wiesenthal Centre’s list of Nazi war criminals still at large.

Tracked down by British historian and author Guy Walters for his book 'Hunting Evil', about the escape and pursuit of Nazi war criminals, she lives in a small apartment on the bank of the Danube in Vienna. Incredibly, her surname is printed on the bell-push for her apartment.

When found by Mr Walters last Friday, Wallisch refused to comment on his investigation into her past as a brutal concentration camp guard.

Other residents in her apartment block said they knew nothing about her history, and most told Mr Walters that they supported the Austrian government’s decision not to prosecute her.

"It’s all in the past and should be forgotten," said Frau Durchhalter, one of Wallisch’s neighbours. "People should learn to forgive."

"I do not find this attitude surprising," said Mr Walters. "For too long, the Austrians have been unacceptably lenient with these evil men and women in their midst. I suspect their reluctance to confront these criminals is because it would only highlight the extent of Austrian complicity with Nazism."

Rarely leaving her home, Wallisch is cared for by her family who bring her groceries and sit drinking coffee and making small talk with their elderly relative.

Born Erna Pfannenstiel, the daughter of a postal clerk in eastern Germany in 1922, Wallisch joined the Nazi party when she was still a teenager and became a camp guard at the Ravensbruck women’s concentration camp near Berlin - where British SOE agent Violette Szabo was among the tens of thousands murdered .

Wallisch later transferred to the Majdanek death camp in Poland where she was based between October 1942 and January 1944. Some inmates claim she beat prisoners to death.

The testimony of at least four has been gathered in a bid to bring justice for her victims.

They allege that Wallisch used "violence and illegal threats for reasons of race and nationality, against women and children weakened physically and psychologically, from peoples within regions under civil occupation ... she treated them in an inhumane way."

In Lublin she had a romance with Georg Wallisch, a Nazi guard, who she later married in March 1944.

Jadwiga Landowska, a former prisoner, recalled how the then-pregnant Wallisch beat people to death.

"The pregnant Nazi monster woman who went crazy and attacked us did not appear among those tried in Duesseldorf after the war. The pregnant one hit a young boy lying on the floor with something harder than a whip. Blood was pouring from his head and he gave no sign of life or reaction. The sweating, breathless face of that monster was something I will never forget."

But Austria’s Justice Ministry has officially informed the head of the Wiesenthal Centre, Dr Efraim Zuroff, that Wallisch’s crimes come under the statute of limitations and she would therefore not be prosecuted.

This reinforces the Centre’s claims, and those of other Nazi hunters, that the Alpine republic has been a haven for Nazis who settled there with little fear of being called to account for their crimes.

In his meeting with Justice Minister Gastinger, Dr Zuroff argued that Wallisch had admitted participation in the mass murder of inmates at Majdanek. But Austria says it can take no legal action against her.

As a result, Dr Zuroff has appealed to the Polish authorities to take action against her based on her own admission that she had committed crimes in Poland and against Polish citizens. There is no statute of limitations for such crimes in Poland.

Dr Zuroff said: "It is unthinkable that a person who was part of the mass murder of at least thousands of innocent civilians should be protected by Austrian law, and we therefore urge the Polish authorities to try to achieve justice in this case."