COLUMBUS, Ohio -- An ex-deep-sea treasure hunter is violating his plea agreement by giving evasive answers about the fate of 500 missing gold coins pulled from an historic shipwreck, say a group of investors who helped fund the hunt for the ship.

Defendant Tommy Thompson went missing three years ago amid demands that he appear in court. He and his longtime female companion were apprehended in January at a hotel where he was living near Boca Raton, Florida.

Thompson has faced accusations of cheating investors since he discovered the S.S. 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.

The 161 investors who paid Thompson $12.7 million to find the ship never saw any proceeds. Two sued -- a now-deceased investment firm president and the company that once published The Columbus Dispatch newspaper.

Thompson pleaded guilty in April to contempt of court for failing to appear before a federal judge in 2012. Part of his plea deal requires him to answer questions in closed-door sessions about the whereabouts of the gold coins.

The first of those hearings was Oct. 19. A federal prosecutor chastised Thompson afterward, calling his answers evasive and concerning, and scheduled another hearing for Oct. 26.

But Thompson's former attorney cancelled the hearing two days beforehand, saying he told Thompson not to answer further questions at the risk of incriminating himself. That attorney, Steve Nolder, no longer represents Thompson, and declined to comment. A message was left with Thompson's new attorney.

Thompson was criticized by investors for "feigned ignorance, convenient lack of recollection, and then outright refusal to answer any more questions," according to a court filing last week.

Thompson can't say whether the coins are on the island of Nevis, in Belize or elsewhere, and who he gave them to for moving them out of the country, the filing said. The coins are worth between $2 million and $4 million.

"In short, Thompson would have us believe that he gave millions of dollars of gold coins to a complete stranger, to be transported to Belize, Nevis or some other foreign location, but he does not know where in the world the coins were taken, how they got there, where they are now, who is charged with protecting them, or how to access them," the investors said.

Thompson faces two years in prison and a maximum fine of $250,000 at his Nov. 24 sentencing.