Former Bixby Energy Systems CEO Robert Walker pleaded not guilty Thursday to a revised federal indictment that adds witness tampering to earlier charges of mail fraud, wire fraud, tax evasion and conspiracy.

Walker, 70, is accused of bilking 1,800 investors, business partners and customers of the failed Ramsey, Minn.-based company, pitching a “clean coal” technology that federal officials say he knew never worked.

Walker, who had been out on bail, was ordered back to jail in August by a judge who cited witness tampering. Walker is scheduled to go on trial in January in U.S. District Court in Minnesota.

David Shaffer