A US treasure hunter who was imprisoned for 10 years after refusing to reveal the location of missing gold coins has been released from prison, without officials apparently ever learning where that gold is.

Tommy Thompson – a renowned salvager who in 1998 found the long-lost, so-called Ship of Gold near South Carolina – was freed from federal prison on 4 March, records and reports recently indicated.

The ship sailed under the name SS Central America before Thompson, now 73, found it with tons of “sunken treasure” inside, CBS News said.

The SS Central America was transporting more than 400 passengers and crew as well as 30,000lb of federally minted gold when it sank in 1857. Thompson and his team found the ship about 7,000ft below the surface, at the bottom of the Atlantic Ocean, as CBS News reported.

Investors who funded Thompson’s search for the ship later claimed that he bilked them out of their cut of the treasure, and they sued him in 2005.

Thompson insisted that he didn’t know where 500 coins made from the ship’s gold were in particular. He “went into seclusion” in Florida and was deemed a fugitive when an Ohio federal judge issued a warrant to arrest him for skipping a court date, CBS News reported.

Authorities found Thompson three years later, living in a Florida hotel under an assumed name. The judge reportedly held Thompson in contempt and sent him to prison after he refused to answer questions about the coins’ whereabouts.

Thompson repeatedly claimed that the $2.5m in coins had been given to a Belize-based trust – and that $50m from selling an initial set of gold largely paid for bank loans and legal fees.

Although federal laws typically limit prison for contempt to 18 months, US appellate judges decided in 2019 that Thompson’s case was an exception. They found that Thompson’s refusal was in violation of a plea agreement.

During another plea for release in 2020, Thompson reportedly told a judge: “Your honor, I don’t know if we’ve gone over this road before or not, but I don’t know the whereabouts of the gold.” He also said: “I feel like I don’t have the keys to my freedom.”

The investors’ lawsuit against Thompson was dismissed in 2018. More recently, a judge decided to end Thompson’s contempt sentence more than a year before his release, finding that he no longer believed keeping him behind bars would yield information about the gold’s whereabouts, as CBS News noted.

Thompson was then ordered to begin serving a two-year sentence for missing the 2012 court proceeding, and he was released after completing that punishment.