BADEN-BADEN, Germany - Karl Lotter, a prisoner who worked in the hospital at Mauthausen concentration camp, had no trouble remembering the first time he watched SS doctor Aribert Heim kill a man.
It was 1941, and an 18-year-old Jew had been sent to the clinic with a foot inflammation. Heim asked him about himself and why he was so fit. The young man said he had been a soccer player and swimmer.
Then, instead of treating the prisoner's foot, Heim anesthetized him, cut him open, castrated him, took apart one kidney and removed the second, Lotter said. The victim's head was removed and the flesh boiled off so that Heim could keep it on display.
"He needed the head because of its perfect teeth," Lotter, a non-Jewish political prisoner, recalled in testimony eight years later that was included in an Austrian warrant for Heim's arrest uncovered by The Associated Press.
"Of all the camp doctors in Mauthausen, Dr. Heim was the most horrible."
But Heim managed to avoid prosecution, his American-held file in Germany mysteriously omitting his time at Mauthausen, and today he is the most wanted Nazi war criminal on a list of hundreds who the Simon Wiesenthal Center estimates are still free.
Heim would be 93 today and "We have good reason to believe he is still alive," said Efraim Zuroff, the Simon Wiesenthal Center's top Nazi hunter.
He spoke in a telephone interview from Jerusalem ahead of the center's plans to release a most-wanted list today, and to open a media campaign in South America this summer highlighting the $485,000 reward for Heim's arrest posted by the center along with Germany and Austria.
The hunt for Heim has taken investigators from the German state of Baden-Wuerttemberg all around the world. Besides his home country of Austria and neighboring Germany where he settled after the war, tips have come from Uruguay in 1998, Spain, Switzerland and Chile in 2005, and Brazil in 2006, said Heinz Heister, presiding judge of the Baden-Baden state court, where Heim was indicted in absentia on hundreds of counts of murder in 1979.
Thousands of German war criminals were prosecuted in West Germany after World War II. In the 1970s Western democracies began to hunt in earnest for Eastern European collaborators who had fled West claiming to be refugees from communism, and the end of the Cold War gave access to a trove of communist files in the 1990s.
"All of a sudden there was pressure on countries like Latvia and Estonia to put these people on trial," Zuroff said. "So two times in the past 30 years we've been given a tremendous infusion of new energy and new possibilities."
Still, a lack of political will in many countries, and what Zuroff called the "misplaced-sympathy syndrome" - reluctance to pursue aging suspects - has meant that few people have been brought to trial and convicted.
Lotter, the witness to Heim's atrocity, was in Mauthausen because he fought with the communists in the Spanish Civil War. His statement from the 1950 arrest warrant was viewed by the AP at the National Archives in College Park, Md.
Now that the necessary evidence is in place, numerous witness statements have been taken and Heim has been indicted, all that's left is to find him.