Federal prosecutors have added tax evasion to the list of charges against Bob Walker, whose Ramsey-based company once promised investors they could profit from new technology to turn coal into cleaner-burning gas.

An updated indictment filed Tuesday in U.S. District Court in Minnesota added three fresh allegations that Walker, 70, failed to pay income taxes from 2004-2006 on income, including kickbacks he earned while cheating investors and a Chinese-owned business partner out of $45 million.

The gist of the case against the former CEO of Bixby Energy Systems is unchanged, and still includes mail fraud, wire fraud and conspiracy charges. The new indictment dropped securities fraud charges, though it still alleges that investors were defrauded. A trial is set for September.

He ran the company from 2001 until he was ousted by the board in 2011.

Walker is best known as the founder of Select Comfort and inventor of its signature Sleep Number bed. But the indictment adds a new twist, saying Walker duped investors by "falsely claiming credit for the financial success and the public offering of Select Comfort stock" even though it happened "many years after Walker had left."

His attorney could not be reached to comment.

David Shaffer