COLUMBUS, Ohio (AP) — A former deep-sea treasure hunter is about to mark his fifth year in jail for refusing to disclose the whereabouts of 500 missing coins made from gold found in a historic shipwreck.

Research scientist Tommy Thompson isn’t incarcerated for breaking the law. Instead, he’s being held in contempt of court for an unusually long stretch — well past the normal maximum limit of an 18-month internment in cases of witnesses refusing to cooperate.

But nothing is usual about Thompson’s case, which dates to his discovery of the S.S. Central America, known as the Ship of Gold, in 1988. The gold rush-era ship sank in a hurricane off South Carolina in 1857 with thousands of pounds of gold aboard, contributing to an economic panic.

Despite an investors lawsuit and a federal court order, Thompson still won’t cooperate with authorities trying to find those coins, according to court records, federal prosecutors and the judge who found Thompson in contempt.

“He creates a patent for a submarine, but he can’t remember where he put the loot,” federal Judge Algenon Marbley said during a 2017 hearing.

Thompson’s legal troubles stem from the 161 investors who paid Thompson $12.7 million to find the ship, never saw any proceeds and finally sued.

Back in 2012, a different federal judge ordered Thompson to appear in court to disclose the coins’ whereabouts. Instead, Thompson fled to Florida, where he lived with his longtime female companion at a hotel near Boca Raton. U.S. marshals tracked him down and arrested him in early 2015.

For background on Thompson’s case and footage of the gold treasure, check out the video from NewsNation affiliate WCMH below:

Thompson pleaded guilty for his failure to appear and was sentenced to two years in prison and a $250,000 fine. Thompson’s criminal sentence has been delayed until the issue of the gold coins is resolved.

That April 2015 plea deal required Thompson to answer questions in closed-door sessions about the whereabouts of the coins, which the government says are worth $2 million to $4 million. Importantly, he must also “assist” interested parties in finding the coins under that deal.

Thompson refused several times, and on Dec. 15, 2015, Marbley found Thompson in contempt of court and ordered him to stay in jail — and pay a $1,000 daily fine — until he responds.

In late October of this year, Thompson appeared by video for his latest hearing.

“Mr. Thompson, are you ready to answer the seminal question in this case as to the whereabouts of the gold?” Marbley said.

“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,” Thompson responded. “I feel like I don’t have the keys to my freedom.”

And with that, Thompson settled back into his current situation: housed in a federal prison in Milan, Michigan, he’s now spent more than 1,700 days in jail and owes nearly $1.8 million in fines — and counting. Thompson’s attorney declined to comment.

Thompson, 68, has said he suffers from a rare form of chronic fatigue syndrome that has created problems with short-term memory. He’s previously said, without providing details, that the coins were turned over to a trust in Belize.

The government contends Thompson is refusing to cooperate and that there’s no connection between his ailment and his ability to explain where the coins are.

A federal law addresses individuals like Thompson, known as “recalcitrant witnesses.” The law holds that 18 months is generally the limit for jail time for contempt of court orders. But a federal appeals court last year rejected Thompson’s argument that that law applies to him.

Thompson hasn’t just refused to answer questions, the court ruled: He’s also violated the requirement that he “assist” the parties by refusing to execute a limited power of attorney to allow that Belizean trust to be examined, as required under his plea deal.

“The order isn’t intended to solely seek information, it’s to seek information for the purposes of recovering these unique assets,” said law professor and legal analyst Andrew Geronimo, director of Case Western University’s First Amendment Clinic.

Earlier this year, Marbley denied Thompson’s request for release over concerns he’s at risk for contracting the coronavirus behind bars. Marbley said Thompson didn’t present proper evidence for his risk level, and also noted he remains a flight risk.

The investors still looking for their money say Thompson has no one but himself to blame for his incarceration.

“He would be out of prison by now if he had simply complied with his plea agreement and cooperated in locating missing assets when he was supposed to,” attorney Steven Tigges said in a March court filing.