A former deep-sea treasure hunter who has not disclosed the location of 500 missing gold coins remains in an Ohio jail for the fifth year.

Research scientist Tommy Thompson has been in jail for contempt of court for half a decade – well past the normal maximum limit of 18 months for such cases.

Thompson took on a case for 161 investors who paid him $12.7 million to excavate a sunken ship, the S.S. Central America, which was known as the Ship of Gold and sunk in 1857 during a hurricane off South Carolina.

Thompson took the money but never returned the gold, leading the investors to sue him.

Tommy Thompson (Delaware County Sheriff's Office via AP, File)

After failing to appear in court in 2012 to disclose the coins’ whereabouts, Thompson lived in Florida in hiding for three years before U.S. marshals tracked him to Boca Raton and arrested him.

Thompson pleaded guilty for his failure to appear and was sentenced to two years in prison and a $250,000 fine, but he had to answer questions in closed-door sessions about the coins, which the government estimated to be worth $2-4 million.

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

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“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 told Marbley during a 2017 hearing. “I feel like I don’t have the keys to my freedom.”

“He creates a patent for a submarine, but he can’t remember where he put the loot,” Marbley said.

A federal law on “recalcitrant witnesses” – or people who do not want to cooperate in a trial – holds that 18 months is generally the limit for jail time. However, a federal appeals court last year rejected Thompson’s argument that the law applies to him.

“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.

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

The Associated Press contributed to this report.