BOSTON — The longtime girlfriend and fugitive companion of Boston mobster James “Whitey” Bulger was indicted Tuesday on a charge she refused to testify about whether other people helped him during his 16 years on the run.

Catherine Greig, 64, was indicted by a federal grand jury on one count of criminal contempt.

Greig is already serving an eight-year sentence for conspiracy to harbor a fugitive, identity fraud and conspiracy to commit identity fraud. If convicted of the new charge, Greig could face additional prison time.

The indictment alleges that from December 2014 through Tuesday, Greig refused to testify before a grand jury.

“Catherine Greig has yet again failed to do the right thing,” said Joseph Bonavolonta, acting special agent in charge of the FBI’s Boston division. “Her refusal to testify has hindered the FBI’s efforts to seek justice for the victims of his crimes.”

Bulger fled Boston in 1994 and remained a fugitive until he was captured in Santa Monica, California, in 2011. He had been living with Greig in a rent-controlled apartment.

Bulger, now 86, was convicted in 2013 of participating in 11 murders and is serving a life sentence. Bulger’s life of crime and his role as an FBI informant are depicted in “Black Mass,” a film released last week starring Johnny Depp as Bulger.

When Greig was sentenced for helping him, her lawyer, Kevin Reddington, called Bulger “the love of her life” and said she had no regrets about what she did. Reddington did not immediately respond to calls seeking comment on the new indictment Tuesday.

Prosecutors said Greig helped Bulger evade capture by taking him to medical appointments, posing as his wife so she could pick up his prescriptions and using false identities. They said Bulger and Greig posed as married retirees from Chicago.

When authorities searched their Santa Monica apartment, they found more than $800,000 in cash and 30 weapons, most hidden in holes cut into the walls.

When Bulger first fled Boston, he took with him Teresa Stanley, a woman he’d been romantically involved with since the 1960s. The FBI has said Bulger dated Greig for most of the time he was seeing Stanley.

After about two months on the run, Bulger returned to Boston, dropped Stanley off and picked up Greig, who remained by his side for more than 16 years until their capture.

The charge of criminal contempt carries no fixed maximum penalty.