Catherine Greig, 64, is already serving a sentence in prison for helping Bulger avoid authorities.

In November, U.S. District Judge Denise Casper issued an order demanding that Greig provide details about anyone who helped Bulger hide from 1995 to 2011.

During that time, Bulger and Greig lived as Charlie and Carol Gasko in a seaside apartment in Santa Monica, California. In his letters to author Michael Esslinger, Bulger described that time as "a 16-year honeymoon."

A neighbor who sometimes helped Greig carry groceries described the couple as quiet and polite. When federal agents finally tracked the pair down, they found more than $822,000 in cash hidden inside the walls of the apartment.

After they were arrested in June 2011, Greig pleaded not guilty to harboring and concealing Bulger. (A jury found Bulger guilty on 31 of 32 charges, including 11 murders, in August 2013. Bulger, 86, received two life terms plus five years. His lawyers reportedly argued for an appeal this summer.)

The following year, Greig pleaded guilty to a charge of conspiracy to harbor a fugitive and two counts of identity theft. She was sentenced in June 2012 to eight years in federal prison, a term an appeals court upheld in May 2013.

Bulger's exploits received the Hollywood treatment in the movie, "Black Mass," in which Johnny Depp plays the mobster. Sienna Miller had been slated to play Greig in the movie, but director Scott Cooper told media outlets he had to cut her scenes and the role of Greig because "it came down to narrative choices."