WILMINGTON, Del. (AP) — Federal agents in Delaware have recovered a more than 500-year-old copy of a letter penned by Christopher Columbus that vanished from an Italian library decades ago.

The U.S. Attorney’s Office in Delaware and Homeland Security investigators, who specialize in the recovery of stolen rare books and historic artifacts, announced the find on Wednesday. The letter is one of a few dozen authentic, reprinted copies of Columbus’ original letter, which was handwritten in Spanish in April 1493 and almost immediately reprinted in Latin by the Rome printer Stephan Plannck.

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It’s the fourth such return in recent years after U.S. investigators, tipped off by a rare books expert, determined that several authentic copies of the Columbus letter had been stolen from libraries across Europe without library officials’ knowledge. Investigators called this latest find — “Columbus Letter Plannck I,” which tells of Columbus’ discoveries in the Americas — the most rare of the four.

The letter, which is valued at up to $1.3 million, was found in the hands of a unidentified private collector and ordered returned to the Biblioteca Nazionale Marciana in Venice, Italy, the U.S. Attorney’s office said. Federal investigators, working with the Italian Carabinieri Command for Protection of Cultural Heritage, determined that the collector was “acting in good faith” in buying the letter from a rare book dealer in the United States in 2003.

Plannck’s first edition of the letter, which Columbus addressed just to King Ferdinand of Spain, is exceptionally rare, the U.S. Attorney’s statement explained. Plannck also printed a second edition of a letter Columbus penned to both Ferdinand and Queen Isabella. They were published to spread the news of Columbus’ discoveries in the 1400s.

The Venetian library acquired a copy of Plannck’s first edition around 1875, and investigators think it was stolen from the library more than 100 years later, in the 1980s, the U.S. Attorney’s office said. Unlike other thefts of Plannck’s printed copies, this letter wasn’t replaced with a forgery.

Investigators finally located the stolen first edition last year. The buyer agreed to have it inspected by Paul Needham, a rare book expert at Princeton University. He told CNN he was able to confirm its authenticity in part, by distinctive sewing on the folds used to bind it together. The buyer agreed to turn it over to authorities, and it will soon make its way home to the national library in Venice.

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In June 2018, The United States returned to the Vatican Library another rare copy of a letter written by Columbus. In that case, the stolen artifact had been replaced with a forgery. The letter had been held by Mary Parsons, the widow of David Parsons, an Atlanta actuary who purchased it from a rare book dealer in New York in 2004, unaware it had been stolen from the Vatican, which had acquired it in 1921.

That same year, another stolen copy was returned to the Library of Catalonia in Spain, according to a U.S. Immigration and Customs Enforcement release . Also, in 2016, U.S. authorities recovered an eight-page copy that had been stolen from Riccardiana Library in Florence, Italy, and donated to the U.S. Library of Congress.