Prosecutors said the funeral mask of Lady Ka-Nefer-Nefer went missing from the Egyptian Museum in Cairo about 40 years ago and that it should be returned to its country of origin. The St. Louis Art Museum said it researched the provenance of the mask and legitimately purchased it in 1998 from a New York art dealer.

US District Judge Henry Autry in St Louis sided with the museum.

The US government “does not provide a factual statement of theft, smuggling or clandestine importation,” Autry wrote in the 31 March ruling.

“The Government cannot simply rest on its laurels and believe that it can initiate a civil forfeiture proceeding on the basis of one bold assertion that because something went missing from one party in 1973 and turned up with another party in 1998, it was therefore stolen and/or imported or exported illegally,” the judge wrote.

A message left with Egypt’s Supreme Council of Antiquities was not returned.