In April 2022, soon after Russia invaded Ukraine, two men arrived at the library of the University of Tartu, Estonia’s second-largest city. They told the librarians they were Ukrainians fleeing war and asked to consult 19th-century first editions of works by Alexander Pushkin, Russia’s national poet, and Nikolai Gogol. Speaking Russian, they said they were an uncle and nephew researching censorship in czarist Russia so the nephew could apply for a scholarship to the United States. Eager to help, the librarians obliged. The men spent 10 days studying the books.

Four months later, during a routine annual inventory, the library discovered that eight books the men had consulted had disappeared, replaced with facsimiles of such high quality that only expert eyes could detect them. “It was terrible,” Krista Aru, the director of the library, said. “They had a very good story.”

At first, it seemed like a one-off — bad luck at a provincial library. It wasn’t. Police are now investigating what they believe is a vast, coordinated series of thefts of rare 19th-century Russian books — primarily first and early editions of Pushkin — from libraries across Europe.

Since 2022, more than 170 books valued at more than $2.6 million, according to Europol, have vanished from the National Library of Latvia in Riga, Vilnius University Library, the State Library of Berlin, the Bavarian State Library in Munich, the National Library of Finland in Helsinki, the National Library of France, university libraries in Paris, Lyon and Geneva, and from the Czech Republic. The University of Warsaw library was hardest hit, with 78 books gone.

The books are worth tens to hundreds of thousands of dollars each. In most cases, the originals were replaced with high-quality copies that mimicked even their foxing — a sign of a sophisticated operation. The disappearance of so many books of the same ilk from so many countries in a relatively short period is unprecedented, experts said. The thefts have led libraries to boost security and put dealers on high alert about the provenance of Russian books.

How Russian rare books came to be at the center of a possible multinational criminal conspiracy is a story of money and geopolitics as much as of crafty forgers and lackluster library security. Authorities, librarians and experts in Russian rare books believe the thieves are smaller fish operating on behalf of bigger fish. But who is behind the thefts, and what motivates them, remain open questions.