When I pick up the phone," says Nazi hunter Simon Wiesenthal, "I never know who will be on the other end." Whether the call brings information or a threat on his life, the 68-year-old Wiesenthal does not waver in his determination to bring war criminals to justice and keep alive the memory of the holocaust.

Since his release from Poland's Mauthausen death camp 32 years ago, Wiesenthal's relentless digging has led to the capture of more than 1,000 Nazis, including Adolf Eichmann and death camp commandant Franz Stangl. Wiesenthal also tracked down the Gestapo agent who arrested Anne Frank and her family in 1944. "I have six million clients," he says somberly, referring to the Jews who died in World War II concentration camps. "You can forgive crimes against you personally, but no one is authorized to forgive crimes against others."

To goad the public conscience, Wiesenthal operates the Jewish Documentation Center in Vienna. There, in a modest two-room office funded by Jewish donors, he stores dossiers on Nazi fugitives, and keeps in touch by mail or phone with a worldwide network of informants. Twice a year he travels to the United States to lecture. "I want to build a memento for murderers who may yet be born," Wiesenthal explains. "I have a warning—that the murderers of tomorrow will never have any rest."

Once a promising architect, the Polish-born Wiesenthal saw his father shipped off to a Soviet prison camp in 1939. Two years later he and his wife, Cyla, were imprisoned themselves by the Germans. After the Polish underground provided false papers that enabled his wife to escape, Wiesenthal fled the prison in 1943, but was recaptured several months later. He tried to commit suicide by slashing his wrists, but recovered in a hospital. "After so many years," he murmurs incredulously, "I'll look at the scars on my wrists and think, 'Was this really so?' " In all, Wiesenthal and his wife lost 89 relatives during the holocaust. Reunited after the war, they were their family's sole survivors.

When the cold war began to limit his effectiveness in pursuing Nazis, Wiesenthal turned over most of his files to Israel, but continued to track Adolf Eichmann. Israeli agents located the Nazi executioner in Buenos Aires in 1959, but still could not prove his identity. Wiesenthal shrewdly dispatched photographers to cover the funeral of Eichmann's father. The film was sent to Israel and was instrumental in Eichmann's arrest. Encouraged by his success, Wiesenthal returned to hunting Nazis full-time. "Sometimes I go to the mirror and look at myself," he reflects. "And I think, 'I am proud of you.' After all my experiences I would still begin again as I did in 1945."

The Wiesenthals live in Vienna in a small home with airtight security. ("If you step on the lawn," he says, "an alarm sounds.") Three times a grandfather—their daughter Pauline, 30, is married to a psychiatrist and living in Israel—Wiesenthal continues to resist his wife's pleas to retire. His final manhunt, for Dr. Josef Mengele, the sadistic SS physician known as the Angel of Death, seems far from ended. Mengele, who sent millions to the gas chambers at Auschwitz-Birkenau and killed thousands more in cruel genetic experiments, is believed to be hiding in Paraguay. Doubtful that he will be captured, Wiesenthal consoles himself with the thought that his quarry "will never get a night's sleep." Certainly he will not if it is in Simon Wiesenthal's power to prevent it, and that is what keeps Wiesenthal going. "When you know your office is the last office," says the old Nazi hunter ruefully, "and that you are the last man who knows the job, then you cannot close down the office and stop."