The concentration camp guards stood with their rifles ready, awaiting the order to fire at Simon Wiesenthal (search) and other prisoners standing along the edge of a pit where their bodies would topple. The future Nazi hunter waited to die. And waited.

Hours later, after many of the condemned slumped in exhaustion, the camp commandant strolled to the line and delivered a reprieve: Soviet troops were coming and the prisoners would be taken away.

"We thought we were going mad," Wiesenthal wrote after World War II (search). "Perhaps we feared [or hoped] we were mad already."

Wiesenthal, who died Tuesday in his sleep at his Vienna home at age 96, was driven by his memories of the Holocaust to fight for justice for its victims, dedicating himself to tracking down Nazi war criminals and to being a voice for the 6 million Jews who perished.

"I think he'll be remembered as the conscience of the Holocaust. In a way he became the permanent representative of the victims of the Holocaust, determined to bring the perpetrators of the greatest crime to justice," said Rabbi Marvin Hier, dean and founder of the Simon Wiesenthal Center in Los Angeles.

Wiesenthal lost 89 relatives during the war. He survived five Nazi concentration camps and seven other prisons, weighing just 99 pounds when a U.S. Army armored unit liberated him and other inmates at Mauthausen (search) in May 1945.

Enlisted by the Americans to research war criminals, the architect pursued the mission long after Allied forces lost interest.

Wiesenthal spent more than 50 years hunting Nazi war criminals, speaking out against neo-Nazism and racism, and remembering the Jewish experience as a lesson for humanity. He estimated he helped bring some 1,100 Nazi war criminals to justice.

"When history looks back I want people to know the Nazis weren't able to kill millions of people and get away with it," he once said.

Israeli President Moshe Katsav praised Wiesenthal as the "biggest fighter" of his generation. Former German Chancellor Helmut Kohl noted the Nazi hunter personally "felt the shadow of history in its brutality."

Wiesenthal was first sent to a concentration camp in 1941, outside Lviv in what is now Ukraine. In October 1943, he escaped from the Ostbahn camp just before the Germans began killing all the inmates. He was recaptured in June 1944 and sent to Janwska, but escaped death when his SS guards retreated with the prisoners to escape Soviet troops.

Wiesenthal's quest began when he was freed by the Americans. He said he realized "there is no freedom without justice," and decided to dedicate "a few years" to that mission. "It became decades," he said.

Even after turning 90, Wiesenthal continued to remind and to warn. While appalled at atrocities committed by Serbs against ethnic Albanians in Kosovo in the 1990s, he said no one should confuse the tragedy there with the Holocaust.

"We are living in a time of the trivialization of the word 'Holocaust,'" he told The Associated Press in 1999. "What happened to the Jews cannot be compared with all the other crimes. Every Jew had a death sentence without a date."

He was troubled recently by deteriorating relations between Muslims and Jews in Europe and by a rise in anti-Semitism on the continent, said Shimon Samuels, the Wiesenthal center's director for international affairs.

"That was the greatest disappointment for a man who had invested his whole life in this," Samuels said.

Wiesenthal's life spanned a violent century.

He was born on Dec. 31, 1908, to Jewish merchants at Buczacs, a town near Lviv in what was then the Austro-Hungarian empire. He studied in Prague and Warsaw and in 1932 received a degree in civil engineering.

He apprenticed as a building engineer in Russia before returning to Lviv to open an architectural office. The Russians occupied Lviv, then the Germans marched in and the terror began.

After the war, working first with the Americans and later from a cramped Vienna apartment packed with documents, Wiesenthal tirelessly pursued war criminals.

He was perhaps best known for his role in helping find one-time SS leader Adolf Eichmann, who organized the extermination of the Jews. Eichmann was tracked to Argentina, abducted by Israeli agents in 1960, and tried and hanged by Israel.

Wiesenthal often was accused of exaggerating his role in Eichmann's capture, although he never claimed sole responsibility.

Eichmann's capture "was a teamwork of many who did not know each other," Wiesenthal told the AP in 1972. "I do not know if and to what extent reports I sent to Israel were used."

Among others Wiesenthal tracked down was Austrian policeman Karl Silberbauer, who he believed arrested the Dutch teenager Anne Frank and sent her to her death at the Bergen-Belsen concentration camp.

That pursuit began in 1958 after a youth told Wiesenthal he did not believe in Frank's existence and murder, but would if Wiesenthal could find the man who arrested her. The search led to Silberbauer's arrest in 1963.

Wiesenthal never caught up with one prime target — Dr. Josef Mengele, the infamous "Angel of Death" at Auschwitz, who died in South America in 1979.

Wiesenthal's quest for justice sometimes stirred controversy.

In Austria, which took decades to acknowledge its role in Nazi crimes, Wiesenthal was ignored and often insulted. In 1975, Chancellor Bruno Kreisky, himself a Jew, suggested Wiesenthal was part of a "certain mafia" seeking to besmirch Austria and even claimed Wiesenthal collaborated with Nazis to survive.

Ironically, Wiesenthal finally won esteem in Austria as a result of the international furor over the election of Kurt Waldheim as president in 1986 despite lying about his past as an officer in Hitler's army.

His refusal to call Waldheim a war criminal drew criticism from outsiders, but Austrians saw that he did not indiscriminately condemn everyone who took part in the Nazi war effort. Wiesenthal did demand Waldheim's resignation, seeing him as a symbol of those who suppressed Austria's role in the war, but he turned up no proof that Waldheim took part in war crimes.

Even after turning 90, Wiesenthal worked regularly at the small downtown office of his Jewish Documentation Center.

"The most important thing I have done is to fight against forgetting and to keep remembrance alive," he said in the 1999 interview with AP. "It is very important to let people know that our enemies are not forgotten."

Wiesenthal's wife, Cyla, died in 2003. Their daughter, Paulinka Kreisberg, lives in Israel, where Wiesenthal will be buried Friday. A memorial service was scheduled in Vienna on Wednesday.