The tip came in an e-mail from the home office in Los Angeles, the headquarters of a human rights organization that promotes tolerance around the world.
It sent Efraim Zuroff and an informal network of associates on a hunt from Jerusalem to Scotland to Hungary. In Budapest, they found the subject of their search: Sandor Kepiro, a frail old man living quietly across the street from a synagogue.
Zuroff wanted him thrown in jail for crimes committed in 1942. It didn't matter that Kepiro was 92 and that some Hungarians appealed for mercy on his behalf.
"Misplaced sympathy is what I'm up against all the time," Zuroff said.
Sympathy defines the broader mission of Zuroff's employer, the Simon Wiesenthal Center, proprietor of the Museum of Tolerance. But the sentiment does not always extend to the nonprofit's more specific, unfinished task: tracking down the last of the suspected Nazi-era war criminals, Kepiro among them.
"We are not tolerant toward Nazis," said Rabbi Marvin Hier, the center's founder and dean.
Named for the legendary Nazi hunter who died last year, the center has focused mainly on education since its 1977 launch, stoking vigilance against anti-Semitism, hate and terrorism.
Its sobering museum is popular with adult tourists and local school groups alike. The center's Moriah Films has won two Academy Awards, for the documentaries "Genocide" and "The Long Way Home."
But the organization still devotes $500,000 of its $29-million annual budget to the grittier business of ferreting out former Nazis and their collaborators.
The effort has drawn fresh attention because of the recent deportation of an 84-year-old San Francisco woman who served as a concentration camp guard. Zuroff, the center's Israel director, has demanded that Germany prosecute her.
For years, the Simon Wiesenthal Center and a federal agency that investigates alleged war criminals have confronted the question of whether enough time had passed to leave them alone, to spare them in their dotage. Today, with most of the suspects in their 80s and 90s, the query's moral complexities may seem all the more compelling.
Not to the pursuers, however. They say the answer remains simple, the choice between clemency and accountability enduringly clear.
"Many well-meaning people might say, 'Why don't you let bygones be bygones?' " Hier said. "There are some who would prefer that we be entirely in the area of tolerance. But this is a two-prong approach."
The turning of the calendar presents practical challenges as well, from paper trails gone cold to a scarcity of living witnesses to the reluctance of numerous governments to move against suspects.
False leads are another obstacle. The center routinely fields erroneous reports on German-speaking fathers-in-law, rude neighbors or feuding business partners.
"I get all kinds," said Aaron Breitbart, a researcher who screens tips that trickle into the center's South Roxbury Drive office.
On the shelf of his cluttered cubicle are two binders containing the identities of war criminals. Upstairs is a list of SS officers.
"I would rather clear somebody than condemn him," Breitbart said. "It's very easy to make an accusation."
Most of the center's work is in Europe, where several thousand suspects are believed to be living out their final days in law-abiding obscurity.
Dozens more probably are scattered across the United States, authorities say.
The center has posted $250,000 bounties -- from a pair of anonymous donors -- for the two most wanted men: Aribert Heim, a supervisor of inhuman medical experiments on concentration camp inmates, killing many; and Alois Brunner, deputy to Holocaust architect Adolf Eichmann.
It is uncertain whether Heim and Brunner are alive; both would be in their 90s. Heim was rumored to have been in Spain. Brunner was last seen in Syria.
Tracking the last Nazis
Finding any Third Reich perpetrator has become largely an archivist's job. The center continues to mine mountains of Nazi military and police records and concentration camp rosters. Many of those sources did not surface until after the fall of the Soviet Union.
Names of suspects are checked against microfilm of Red Cross refugee logs that include immigration destinations for war criminals. German and Austrian Nazis tended to go underground in Europe or flee to Latin America and the Middle East. Their Eastern European collaborators favored the United States and other English-speaking democracies.
A quarter-century ago, the center was spending more than $2 million a year on the search. The amount dwindled as the biological clock thinned the ranks of the unpunished. Zuroff and a German researcher are the center's only full-time Nazi hunters.
The organization's leaders say more money could speed the chase. But they appear squeamish about the notion of tailoring a fund-raising drive around it.
Such a campaign would detract from the center's primary goal of preventing another genocide, said Rabbi Abraham Cooper, the associate dean.
"But would it be great to have three Effie Zuroffs? Yes," he added.
Cooper was sitting in the Los Angeles office beside a box of yellowing documents on former SS Capt. Erich Priebke, 93, who had been a longtime target of the center. Priebke is now under house arrest in Italy for participating in the slaughter of 335 men and boys at the Ardeatine Caves near Rome.
The center has learned to savor victories such as the Priebke case, even if he is not in a jail cell. Over the years, some foreign governments have hesitated to prosecute elderly suspects or keep them in jail after convictions.
In 2002, the center rolled out Operation Last Chance, which offers cash rewards for information on suspects. Its moniker reflects a determination to capture as many people as possible before they die.
"We're in a race against time," Hier said.
Last Chance is co-sponsored by Targum Shlishi, a Florida-based foundation funded by Jewish activist Aryeh Rubin. The operation has zeroed in on Germany, Austria and seven former Soviet bloc countries. It has collected reports on more than 450 people, about 90 of them deemed credible enough to alert authorities.
Informants have recently fingered two men in the United States: a Ukrainian and a Romanian. Their wartime actions have not been verified, and they have yet to be arrested or publicly identified.
The Justice Department's Office of Special Investigations is responsible for apprehending war criminals in the United States; this is the only country to receive the center's "A" grade for Nazi hunting.
Deportation is the stiffest U.S. penalty because the government does not have jurisdiction to prosecute. The Special Investigations squad has deported about 60 people since 1979.
It has allowed several war criminals to stay in the country because of poor health. The Wiesenthal Center endorses medical reprieves when an independent physician confirms that the patient is terminal, or mentally incompetent.
In August, the government sent Elfriede Rinkel, a San Francisco octogenarian, back to her native Germany after a painstaking examination of Nazi personnel records revealed that she had been a guard at the Ravensbruck camp for women.
Rinkel moved to the United States in the late 1950s and married a Jewish Holocaust survivor, who died two years ago.
News reports said she had told nobody about her past, including her husband. One quoted a neighbor as saying her deportation was "cruel."
Not so, said Eli Rosenbaum, who heads the Office of Special Investigations and personally interrogated Rinkel.
"The nature of the underlying conduct requires government action no matter how late the date," he said. "We want perpetrators of crimes against humanity to see pictures in the newspapers of white-haired old men who thought they got away with it."
But Rosenbaum acknowledged that it was "uncomfortable and awkward" grilling the grandmotherly Rinkel.
"I don't think it's possible to have absolutely no sympathy for senior citizens," Rosenbaum said.
"I wouldn't allow myself to have sympathy," he said by telephone from Jerusalem. "You need a certain degree of perseverance and inner strength to put that aside."
Found in phone book
The tip that led Zuroff to Sandor Kepiro's doorstep last year initially pointed to a suspect in Scotland. In the e-mail to the center's L.A. office, a Scotsman said a Hungarian immigrant had boasted of helping the Nazis deport Jews from Hungary.
While trying to confirm the account, Zuroff enlisted a Scottish journalist to interview the Hungarian man, who subsequently told of having contact with Kepiro, a gendarmerie officer convicted in the 1940s for his role in the murder of 1,000 people in Novi Sad, Yugoslavia (now Serbia).
Kepiro apparently never went to prison, and the center did not know his whereabouts, Zuroff said. But after the information from Scotland placed him in Hungary, the next step was easy: He was listed in the Budapest phone book. Like many alleged war criminals, he had not bothered to change his name.
In September, Zuroff called a news conference at the synagogue across from Kepiro's home to expose him. Zuroff also has provided the Hungarian government with documentation of Kepiro's convictions in the Novi Sad massacre.
Kepiro has denied involvement in the killings. He has not been arrested, and a Hungarian court is considering whether to retry him.
Meanwhile, six weeks after the start of Operation Last Chance in Hungary, Zuroff received a letter from the brother of a Holocaust victim. The tip took Zuroff to Australia.
He came face to face there with the family anguish that can result when a beloved father and grandfather is suddenly identified as a suspected war criminal.
Zuroff had located Charles Zentai in the Perth area. The 84-year-old has been implicated in the murder of an 18-year-old Jewish man in Budapest. Zentai, whose original family name is Steiner, moved to Australia in 1950.
He is a widower and retired psychiatric nursing superintendent, and has never been in trouble with the law in his adopted country, relatives say. Now he is fighting extradition to Hungary.
Zentai's four children insist he is innocent. Last February, three of them met with Zuroff at a riverside cafe to state their case. It did not go well.
"He wasn't willing to consider anything other than what he already had on his mind," Ernie Steiner, Zentai's son, said of Zuroff. "He's quite happy to see people suffer through this whole process."
Steiner said his father had left Budapest the day before the young man was murdered. He also said Zentai has a diseased heart and failing memory.
"I've had a lot of people come up to me and say, 'It's too long ago,' " Steiner said. "Labeling my father a Nazi -- that's a trial and torture in itself."
Zuroff said he has heard it all before. While in Australia, he said, he kept his thoughts trained on the October 1944 killing of Peter Balazs.
A Hungarian soldier dragged Balazs off a streetcar because he wasn't wearing the Nazi-mandated yellow star. The soldier took Balazs to a barracks, beat him to death with two colleagues, and threw his body in the Danube River.
The soldier was Zentai, Zuroff said.
"I have a certain sense of what these people are going through," he said of Zentai's family. "It's a terrible shock to them."
But his sympathy stops firmly at the children. He said he is worried that Zentai will manage to fend off extradition until he can die in freedom
Zuroff said Zentai was able to delay his hearing. "We want him put on trial," he said.
Back in Los Angeles, Breitbart, the center's researcher, pondered the appropriate punishment for someone Zentai's age or older.
In general, Breitbart said, he supports the death penalty for crimes against humanity, but there are shadings.
"Do you execute 90-year-old people?" Breitbart said. "Interesting question.
"They should be given the death sentence, but perhaps they should be kept in jail awaiting their death sentence until they die."
He cited an exception: If Adolf Hitler were alive, he would be 117.
"And if they asked me to be the hangman," Breitbart said, "I would do it."