The Swiss Federal Intelligence Service will grant access to the files on Nazi war criminal Josef Mengele, after years of rejecting repeated requests by historians who sought to see if the German death camp doctor spent time in Zurich when there was an international arrest warrant against him.

Mengele, who has been dubbed the ‘Angel of Death’ for his sadistic experiments on inmates at the Auschwitz II-Birkenau concentration camp, fled to South America after World War II but subsequently returned to Europe as a tourist when he visited Switzerland at least once for a ski vacation with his son in 1956.

Historians have long suspected Mengele returned to Europe — specifically Switzerland — after West Germany issued an arrest warrant in 1959.

Researchers found that his wife rented an apartment in Zurich close to the international airport, and local police observed an unidentified man entering the flat.

The decision to open the files announced earlier this month followed a public legal appeal by a historian after years of Swiss rejections.

No date was announced for the lifting of the restrictions.

Mengele served as chief physician at Auschwitz from 1943 to 1944, and was in charge of the camp’s selection process, choosing who would live and who would die.

He sent about 400,000 people to their deaths in the gas chambers, according to the Yad Vashem Holocaust Museum.

The SS captain was also responsible for the medical experiments performed on camp prisoners.

Like many other Nazi officers, Mengele initially fled Europe using Red Cross travel documents obtained under a false identity at the Swiss consulate in Genoa, Italy.

He died in Brazil in 1979, aged 67, without having ever been prosecuted for his crimes, despite Argentine authorities’ knowledge of his true identity.