The St. Louis Art Museum should be able to keep an ancient Egyptian mummy mask now that the Department of Justice has conceded the fight to return it to its native land, reports the St. Louis Post-Dispatch.

The 3,200-year-old mask was purchased from Phoenix Ancient Art, a New York dealer in antiquities, by the museum in 1998 for $499,000. The museum claims to have thoroughly vetted the purchase with organizations including Interpol and the Art Loss Register before finalizing the deal. The museum believes the mask was part of a private collection in the 1960s before being sold in Switzerland to a Croatian collector, making its way to New York in 1995.

However, the Egyptian government claims the artifact has a less straightforward provenance. After being discovered in 1952 at the tomb of Egyptian noblewoman Ka-Nefer-Nefer, who lived in the court of Ramses II, the excavated mask was placed in storage, where it is thought to have disappeared between 1966 and 1973.

Since learning of the mask’s whereabouts in St. Louis in 2006, Egypt has been agitating for its return. The US government sued the institution on the country’s behalf, but the suit was rejected in 2012.

“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,” wrote US District Judge Henry Autrey at the time. US Attorney Richard Callahan admitted to the Post-Dispatch that the evidence of theft is lacking, showing only that after a certain point, “the mask was not in the possession of the Egyptian authorities anymore and there was no paperwork to support the theory that it lawfully left.”

A court of appeals upheld the ruling last month, and an appeal would have had to have been filed by Monday. “The Department of Justice will take no further legal action with respect to the mask of Ka-Nefer-Nefer,” said Callahan.

The main shortcoming of the case, wrote appeals Judge Diana E. Murphy, was the failure to show that the St. Louis Art Museum “knew or were willfully blind to facts including the mask’s ownership by Egypt, ineligibility for private ownership, and lack of a proper license.”