The indictment, filed by the California Attorney General's Office, alleges four counts of forced sodomy, four counts of sexual penetration by force, two counts of forcible rape, one count of forced oral copulation, one count of false imprisonment and one count of criminal threats.
The indictment also charges Gressett, 52, a former senior deputy district attorney, with numerous enhancements alleging he used an ice pick and a handgun and tied or bound the alleged victim.
The 13 counts of forced sexual activity allegedly took place on May 8, 2008, at Gressett's home in Martinez.
Gressett was arrested six months after the alleged rape. He was placed on administrative leave after his arrest on Oct. 2, 2008, and then fired from the district attorney's office on July 24.
The sexual assault charges were initially filed in Contra Costa County Superior Court last year and Gressett pleaded not guilty in November 2008.
The attorney general's office investigated the allegations because Gressett is a county prosecutor, and called 35 witnesses during the grand jury proceeding.
Gressett is free on $1 million bail and is scheduled to be arraigned Nov. 2 on the 13 charges and the enhancements in the indictment. His attorney, Dan Russo, was not immediately available for comment this morning.