He was a pious Muslim convert who went to the Al-Azhar mosque daily, living in Cairo, Egypt, until his death in 1992.

And he was also one of the most monstrous Nazi war criminals still at large, who performed medical experiments on imprisoned Jews in the Mauthausen concentration camp: Fate of Dr. Aribert Heim, the Most-Wanted Nazi War Criminal, Is Uncovered.

CAIRO — Even in old age the imposingly tall, athletic German known to locals as Tarek Hussein Farid maintained the discipline to walk some 15 miles each day through the busy streets of Egypt’s capital. He walked to the world-renowned Al Azhar mosque here, where he converted to Islam, and to the ornate J. Groppi Cafe downtown, where he ordered the chocolate cakes he sent to friends and bought the bonbons he gave to their children, who called him Uncle Tarek.

Friends and acquaintances here in Egypt also remember him as an avid amateur photographer who almost always wore a camera around his neck, but never allowed himself to be photographed. And with good reason: Uncle Tarek was born Aribert Ferdinand Heim, a member of Hitler’s elite Waffen-SS and a medical doctor at the Buchenwald, Sachsenhausen and Mauthausen concentration camps.

It was behind the gray stone walls of Mauthausen, in his native Austria, that Dr. Heim committed the atrocities against hundreds of Jews and others that earned him the nickname Dr. Death and his status as the most wanted Nazi war criminal still believed by the Simon Wiesenthal Center to be at large.

Dr. Heim was accused of performing operations on prisoners without anesthesia; removing organs from healthy inmates, then leaving them to die on the operating table; injecting poison, including gasoline, into the hearts of others; and taking the skull of at least one victim as a souvenir. After living below the radar of Nazi hunters for more than a decade after World War II — much of it in the German spa town of Baden-Baden where he had a wife, two sons and a medical practice as a gynecologist — he escaped capture just as investigators closed in on him in 1962.