COLUMBUS, Ohio (AP) — A federal judge is warning an ex-treasure hunter that he could face another contempt-of-court charge if he doesn't reveal the location of 500 missing gold coins.

Ohio Judge Algenon Marbley on Friday ordered Tommy Thompson to cooperate by granting power of attorney to allow the government to figure out if a trust in Belize knows the coins' whereabouts.

The Columbus Dispatch reports (http://bit.ly/2pMTlLB ) that Marbley refused Thompson's request to appoint a civil attorney to help him review records.

Marbley has held Thompson in contempt of court since December 2015 for violating terms of a plea deal by refusing to respond to questions about the coins' locations.

The coins, valued up to $4 million, were minted from gold taken from the S.S. Central America, which sank in an 1857 hurricane.

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Information from: The Columbus Dispatch, http://www.dispatch.com