Goldman Sachs Group Inc. has always closely guarded the secrets of its lucrative high-speed trading system. Now the securities firm is getting a help from an unusual source: federal prosecutors.

Federal prosecutors in Manhattan this week asked a federal district judge to seal the courtroom at the forthcoming trial of a former Goldman computer programmer accused of stealing the firm's computer code. The move was a formal request to empty the courtroom of the general public when details of Goldman's trade secrets are being discussed....