(CNN) The United States returned a rare copy of a letter by Christopher Columbus describing his discoveries in the New World, after it had been stolen from a museum in Spain.

The investigation into the stolen letter spanned seven years and on Wednesday it was transferred back to Spanish authorities during a repatriation ceremony, according to the US Immigration and Customs Enforcement.

ICE, which investigates looted cultural heritage and stolen artwork, and the Department of Justice worked on the case after receiving a tip in 2011 that several manually printed copies of the letter had been stolen from European libraries.

Known as the Catalonia Plannck II Columbus Letter, it contains the explorer's 1493 account of his discoveries, addressed to King Ferdinand and Queen Isabella of Spain. Only about 80 copies of all editions have survived.

Investigators learned that one of the copies had been stolen from the National Library of Catalonia in Barcelona and determined in 2012, that the one at the library was a forged copy.

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