A decade ago, an employee stole 25 priceless documents from the Netherlands’ National Archives in the Hague. The trove included 16th-century records of clandestine government affairs, a 15th-century letter from a knight and documents from the Dutch East India Company.

Officials weren’t aware the documents had been stolen until recently, when they were returned by the Amsterdam police and art detective Arthur Brand, who is known for recovering lost and stolen artworks and artifacts. //

Officials at the archives knew that the documents were missing, but they assumed they had simply been misplaced. “We manage more than [90 miles] of archives, over 15 million photographs and 300,000 maps and drawings,” a spokesperson for the National Archives tells NL Times. “With such numbers, it is impossible to have a complete inventory of all the documents.”