Greg Morvillo, a lawyer for Chiasson, and Steve Peikin, a lawyer for Horvath, didn't return voice-mail messages yesterday seeking comment on the charges.
Sigma is a division of SAC Capital Advisors LP. Jonathan Gasthalter, a spokesman for Stamford, Connecticut-based SAC, declined to comment on the superseding indictment.
The three men pleaded not guilty and face trial before U.S. District Judge Richard Sullivan on Oct. 29. Securities fraud carries a term of as long as 20 years in prison.
Prosecutors said in court after Chiasson's arrest on Jan. 18, that he used inside information to win for his Level Global fund what the U.S. said was a single "enormous bet" of $53 million on Dell trades.
The case is U.S. v. Newman, 12-00124, U.S. District Court, Southern District of New York (Manhattan).