People pass a sign for JPMorgan Chase at it's headquarters in Manhattan, New York City.

The criminal sentencing of former J.P. Morgan Chase precious metals trader John Edmonds has been postponed six more months, to December, as federal investigators continue to probe possible manipulation of metals markets.

Edmonds, 37, pleaded guilty in October in Connecticut federal court to working with other "unnamed co-conspirators" to manipulate the prices of gold, silver, platinum and palladium futures contracts between 2009 and 2015 while employed at J.P. Morgan.

The New York City man admitted learning illegal trading tactics from senior traders — and to using those tactics with the knowledge and consent of supervisors.

His sentencing has been postponed twice, suggesting he is continuing to cooperate with prosecutors in their investigation. No one else has been charged.

Edmonds' attorney could not be reached for comment.

On the heels of his plea, multiple lawsuits were filed against J.P. Morgan and the bank's metals traders accusing the bank of illegally manipulating precious metals markets for years. Edmonds' admissions also echo allegations made in a similar, 2015 suit filed against the bank by a hedge fund manager and two commodity traders.

All of the lawsuits were put on hold until May 31 by the federal judges overseeing each case at the request of prosecutors, who argued they could interfere with the criminal probe.

Prosecutors plan to request an extension of the stay in the civil suit proceedings, a source said.

J.P. Morgan for the first time in February mentioned the legal actions in a financial disclosure, saying "various authorities, including the Department of Justice's Criminal Division, are conducting investigations relating to trading practices in the precious metals markets and related conduct. The Firm is responding to and cooperating with these investigations."

J.P. Morgan declined to comment when contacted by CNBC.