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.