Aribert Heim was the medical doctor at Mauthausen concentration camp in Austria. He was dubbed “Doctor Death” due to the hideous “experiments” he conducted on prisoners, killing many and torturing more.

Despite being arrested and questioned by the Allies immediately after the war, he was released and led a seemingly respectful life as a doctor in Baden Baden, until details of his crimes emerged in the early 1960s.

He fled in 1962 as police moved to arrest him, and has not been seen since.

Now his son Rüdiger, 52, says he and his mother received mysterious notes in their letter box during the following five years.

“Between 1962 and 1967 two notes appeared in our post box. There was a single sentence written on them “I am doing fine.” But whether these letters were really from my father, I don’t know.”

Heim is thought by investigators to be in Chile, where a daughter of his lives, but despite a number of supposed sightings, they have been unable to find him.

Heim junior is adamant he has no idea where his father is. When asked what he would do if he knew, he said, “I would shout out to the whole world that he should give himself up and answer these terrible charges.

“The past of my father is a part of my life. To deny that would be pointless, although I don’t have to explain to anyone that I am no Nazi – anyone who knows me knows that.”

He said he was working with a lawyer to work out how to have his father declared missing and then dead, in order to gain control over the more than one million euros in a Berlin bank under his father’s name.

“We only found out about this bank account in 1997. If I was actually the heir, I would donate the money – for the historical examination of the suffering in the Mauthausen concentration camp.”

Efraim Zuroff, head of the Simon Wiesenthal Centre in Jerusalem is convinced the now 94-year-old is still alive, and living in South America. The Nazi hunter is still trying to find him.

Heim junior said, “I can’t even remember when I saw him for the last time in 1962. I grew up fatherless in the house of my grandparents. I don’t know where he lives, nor do I finance his flight. If he were dead, I would not know where he is buried.”

It was only several years after Heim had fled the wealthy home that his son even learned about his crimes.

“My mother always told me he had left to work as a doctor in Berlin. I believed this story until I was 12 years old. Only then did the suspicion arise, piece by piece, that his absence could have had something to do with the terrible events in the concentration camp. This became certain for me when the allegations against Aribert Heim were made public in the press in 1978.”