Jailed businessman Robert Walker now faces a new allegation — witness tampering — on top of 16 earlier charges related to the Bixby Energy Systems fraud.

A federal grand jury returned a third updated indictment this week, alleging that Walker worked through unwitting supporters and attempted to influence by e-mail a China-based businessman who is slated to testify against him at a trial set for next January.

The indictment, released Wednesday, restates other charges of mail fraud, wire fraud, tax evasion and conspiracy.

Walker, 70, who is credited with developing the Sleep Number bed and founding Select Comfort in the 1990s, is accused in the past decade of raising $57 million from 1,800 Bixby investors who believed his promises that the Ramsey-based company had developed technology to turn coal into cleaner-burning gas. He also is accused of bilking $4.5 million from Chinese customers who signed up to install the technology though Global Partners United (GPU), which licensed the technology in Asia.

In August, U.S. Magistrate Judge Tony Leung ordered Walker, who had been out on bail, to remain in jail indefinitely after finding that he tampered with the GPU witness and violated probation terms.

Walker, who left Bixby in 2011 amid allegations of wrongdoing contained in civil lawsuits, still has loyalists among Bixby investors who don’t blame him for their losses. The indictment alleges that he used three of them in his attempt to influence a Beijing-based executive of GPU, which also had invested $10 million in the Bixby technology.

The indictment alleges the technology never worked and that Walker knew it all along. Two other participants in the fraud already have pleaded guilty and gone to prison in the case.