A grand jury indicted Shayanna Jenkins, 24, on a single count in relation to the investigation into the June 17 killing of Odin Lloyd, Bristol County District Attorney Samuel Sutter said.
It wasn't clear what led to the charge. Sutter's spokesman, Gregg Miliote, said he could not comment until her arraignment, which has not been set. A message left for Jenkins' lawyer was not immediately returned.
Lloyd, a 27-year-old semiprofessional football player from Boston, was found shot to death in an industrial park in North Attleborough, Mass., near Hernandez's home, where Jenkins also lives. Lloyd had been dating Jenkins' sister.
Jenkins was not arrested and will be ordered to appear in court for an arraignment, the prosecutor's office said. She and Hernandez have a young child together.
Hernandez has pleaded not guilty to first-degree murder and weapons charges in Lloyd's death and is being held without bail. His attorneys have said the state won't be able to prove its case during a jury trial and that Hernandez will be exonerated.
Prosecutors say Hernandez killed Lloyd because he was upset with him for talking to some people at a nightclub with whom he had had problems.
Prosecutors said as recently as Thursday that the investigation was ongoing, the grand jury was continuing to hear evidence and that more charges could be coming.
In addition to Hernandez and his girlfriend, three others face charges in the case. Hernandez associate Ernest Wallace has pleaded not guilty to being an accessory to murder after the fact.
Another associate of Hernandez, Carlos Ortiz, also was indicted on the same charge, Sutter said Friday.
Ortiz's attorney, John Connors, said Friday that the indictment wasn't unexpected. He said Ortiz will plead not guilty to the new charge and that he will make an argument for bail but had no further comment. A hearing on the gun charge that was scheduled for Friday was cancelled.
Given the indictment, Ortiz's case now shifts to superior court in Fall River. His arraignment there has not been scheduled.
Hernandez's cousin, Tanya Singleton, also was indicted on a new charge of conspiracy to commit accessory after the fact, Sutter said. Prosecutors say that in the days after the killing, she drove with Wallace from her home in Bristol, Conn., where Wallace had lived at times, to Georgia, where her car broke down, and that she then bought him a bus ticket to Florida, where his family lives.
Singleton had been indicted earlier on a charge of criminal contempt after allegedly refusing to testify before the grand jury hearing evidence in the case. Prosecutors say they offered her immunity.
A message seeking comment was left for her attorney.