It was an accident. In 1995, Michael MacQueen (’80, M.A. ’83) was at work in the dingy state archives of Lithuania, in the capital city of Vilnius, sifting through personnel files of Lithuanians who had served in Nazi death camps in Poland, when he spotted a document that seemed to have been attached by mistake. It reported that two guards at a concentration camp, Majdanek, had received 25 blows of the whip for leaving camp without permission. The reason: They had gone “in pursuit of some salt and onions,” a euphemism for visiting a brothel.

One of the guards was John Demjanjuk. When MacQueen, a historian for the U.S. Justice Department’s Office of Special Investigations (OSI), discovered the document, Demjanjuk already had lost his American citizenship and had been tried and sentenced to death for being the notorious SS guard known as Ivan the Terrible. Later, in 1993, the Israeli Supreme Court overturned the sentence after new evidence showed the conviction was based on a case of mistaken identity.

Now MacQueen had found evidence that placed Demjanjuk back in the death camps and filled the gaps in his service history. A new denaturalization trial followed in 2002. Today, Demjanjuk, age 91, stripped of his U.S. citizenship a second time, is on trial in Munich, accused of being an accessory to the deaths of at least 27,900 people.

MacQueen says that chance encounter with the Demjanjuk document, and others like it during his career as a war crimes investigator, was no fluke. “I like that quote of Descartes, ‘Chance favors the prepared mind,’” he says. “I tend to be methodical.”

That methodical approach led to one denaturalization, four extraditions, and a number of deportations during MacQueen’s two decades at OSI. In 2008, MacQueen moved to the Department of Homeland Security’s U.S. Immigration and Customs Enforcement (ICE). His job at ICE is much the same: to gather evidence that suspected war criminals received their U.S. citizenship by hiding their wartime activities. With the Nazi-era cases largely closed, the suspects he tracks now are from the Balkan wars of the 1990s. MacQueen’s investigations have resulted in 25 individuals losing their American citizenship.

In 2010, the number of worldwide investigations into suspected Nazis rose for the second consecutive year to 852, according to the Simon Wiesenthal Center. Germany saw the most dramatic increase in cases: from 27 to 177. Australia, Canada, and Norway were among countries given failing grades for their investigative efforts.

John Demjanjuk received this service certificate in 1942 as a guard at a training camp in Trawniki, Poland. The writing “27.3.43 Sobibor” notes Demjanjuk’s arrival date at the concentration camp Sobibor, where he is widely suspected of being “Ivan the Terrible,” committing murderous and savage acts against prisoners.

In December 2009, Demjanjuk was led to the courtroom on a stretcher in Munich to face trial. He is formally charged with 27,900 counts of acting as an accessory to murder. Photos: © Marijan Murat/dpa/Corbis; JOHN MACDOUGALL/AFP/Getty Images

MacQueen works out of a cubicle in downtown Washington, D.C., with a map of Bosnia and a photo of him racing a green MG Midget tacked to the walls. The troubled Balkan state is where he spends a couple months a year in his investigations. Road racing is a passion he developed after he dropped out of LSA in 1968.

He spent the decade after dropping out working as a mechanic. At age 28, he re-enrolled at U-M and began his study of ethnic nationalism and ethnic conflict in Eastern Europe, at LSA’s Center for Russian, East European, and Eurasian Studies.

“I was working on my Ph.D. dissertation in Ann Arbor when I saw an ad in the Chronicle of Higher Education. It was lifted right from my résumé.” The Justice Department was looking for a historian to conduct World War II-era research in Eastern Europe. MacQueen was hired in 1988 and headed for Vilnius.

To aid his work, MacQueen, who already spoke German and Polish, taught himself Lithuanian. In recent years, he also added Serbo-Croatian to his toolkit.

He revels in catching the bad guys, saying he finds it “strongly offensive” when someone with a gun is able to commit atrocities with a sense of impunity. But mixed with moral indignation is a delight in his work that has survived more than two decades of dusty archives and unsavory suspects.

“When I finish one case, I box up the stuff and go on to the next one,” MacQueen says. “I’m never going to retire.”