The chief executive of Goldman Sachs, Lloyd C. Blankfein, has emerged as a possible witness in the insider trading trial of Raj Rajaratnam.

Lloyd Blankfein, chairman and CEO of The Goldman Sachs Group, is sworn in while testifying before the Senate Homeland Security and Governmental Affairs Investigations Subcommittee on Capitol Hill.

Mr. Blankfein has agreed to testify for the government in the trial of Mr. Rajaratnam, a founder of the Galleon Group hedge fund, according to a person with direct knowledge of the case who spoke only on the condition of anonymity. Mr. Rajaratnam’s trial is scheduled to start on Tuesday in federal court in Manhattan.