A California man pleaded guilty Friday to swiping a $550,000 gold bar dating back to the 1600s from a museum in Key West, Florida.

Richard Johnson, 41, in an appearance at U.S. District Court in Key West Friday, agreed to plead guilty to two felony counts of theft and testify against the man who prosecutors claim aided the theft by serving as his lookout, the Florida Keys News reported.

Johnson’s guilty plea comes in exchange for a lighter sentence, which has not been determined. The court has not yet scheduled a date for his sentencing.

Johnson drove from West Palm Beach to Key West with an accomplice to steal the nearly five-pound artifact from Key West’s Mel Fisher Maritime Heritage Museum in 2010.

More than seven years later, authorities arrested Johnson and his suspected accomplice, Jarred Alexander Goldman, 32, for theft of major artwork and conspiracy to commit a crime against the United States.

The museum was never able to recover the item and prosecutors have said the gold bar was “likely lost to history.”

Before it was stolen, the museum locked the gold bar in a see-through case that visitors could place their hands through to touch the item.

Prosecutors say video surveillance footage showed Johnson damaging the case enough to crack it open and retrieve the item.

The gold bar was found in a shipwrecked Spanish vessel that sunk during a hurricane in 1622. The vessel was one of 28 that had been on its way to Spain from Havana, Cuba, loaded with silver, gold, and other treasures.