Questions of provenance have grown, thanks partly to the Naples case. Last year, the International League of Antiquarian Booksellers issued a warning for buyers and sellers to check any Italian books from the 15th through 17th centuries purchased in the first half of 2012, in case they had been removed from the Girolamini.
Using techniques perfected in international organized-crime cases, Naples prosecutors are now focusing on rare-book dealers and collectors who may have bought works they probably knew had been taken from the library. They are slowly exposing the practices of the rare-book market, where deception sometimes reigns, prices can reach into the millions of dollars, and the trail often goes dead at the Swiss border.
“The international market absorbed, without batting an eye, books that they couldn’t not have known came from the Girolamini Library,” Giovanni Melillo, the Naples prosecutor who is leading the investigations, said in an interview this week. “The rule ‘don’t ask, don’t tell’ is what governs the rare-book market,” he added. Prosecutors have requested cooperation from across Europe, as well as from the United States and Argentina.
In the widening investigation, in August, police arrested a rare-book dealer in Munich, Herbert Schauer of the auction house Zisska & Schauer, on charges of complicity in receiving books taken from the Girolamini. He is being held in a prison outside Naples and contests the charges.
Other prominent politicians figure in the plot. The lower-court sentence noted that Mr. De Caro had given Marcello Dell’Utri, then a senator and a longtime associate of Mr. Berlusconi’s, several books taken from the Girolamini as gifts, but that Mr. Dell’Utri had been unaware of their provenance. Once the investigation began, Mr. Dell’Utri gave the books back.