Efraim Zuroff has accomplished much in his long career, but there’s one thing he’s particularly proud of: He’s the most hated Jew in Lithuania.

His Lithuanian friend Ruta Vanagaite agrees: She called him a “mammoth,” a “boogeyman” and the “ruiner of reputations”—and that’s just in the introduction to a book they co-authored.

Last summer, in a journey that helped cement his notoriety, Zuroff set off across the Lithuanian countryside in a gray SUV with Vanagaite, an author best known for a book about women finding happiness after age 50. Their goal: to visit some of the nation’s more than 200 sites of mass murder during World War II. On the road, between destinations, they talked and talked, recording their conversations. The trip formed the basis of their 2016 book, Our People: Journey With an Enemy, an instant best-seller in Lithuania. It also ignited a rancorous debate among Lithuanians, who have long downplayed their country’s considerable role in the Holocaust.

Zuroff, often called the last Nazi hunter, has spent nearly four decades chasing down suspects from Australia to Iceland, from Hungary to the United States. His methods are sometimes controversial, but his mission is righteous: bringing to justice every remaining perpetrator of one of the most heinous crimes in history. For Westerners, the tiny country of Lithuania might seem an odd place for him to dig in, but with most Nazis either dead or too frail to face trial, this Eastern European nation may be the Nazi hunter’s last stand. He considers Lithuania one of his most important fights because it hasn’t addressed its role in mass murder during the Holocaust—its citizens killed almost all of the 250,000 Jews who lived there in 1941. “Not a single Lithuanian sat one day in jail in independent Lithuania” for collaborating with the Nazis and participating in the Holocaust, Zuroff tells Newsweek.

“I realize how difficult it could be for Lithuania to admit its complicity,” he told Vanagaite in Our People. “It took France 50 years to acknowledge its guilt. Germany had no choice. But for your sake and your children’s sake, the sooner you face this honestly, the sooner the healing process will start.”

“If it took France 50 years, it will take Lithuania 50 years as well,” said Vanagaite.