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. 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.