BOSTON (CBS) – “Let Catherine free. Free Catherine,” said Margaret McCusker, at the door of her South Boston apartment the day before her twin sister, Whitey Bulger’s gal Catherine Greig, is set to be face sentencing.

Through tears, she insisted her sister is not a criminal. “She met this gentleman and she fell in love with him, and she felt he was her soulmate and she stayed with him, and she’s still with him really.”

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Margaret McCusker, the twin sister of Whitey Bulger's girlfriend Catherine Greig. (WBZ-TV)

Margaret McCusker, the twin sister of Whitey Bulger’s girlfriend Catherine Greig. (WBZ-TV)

Thursday, prosecutors plan to ask a federal judge to sentence Greig to another three years for refusing to cooperate with the investigation. That would be in addition to the eight years she’s already serving for harboring a fugitive.

McCusker says she’s pleaded with Greig to speak with authorities in order to be freed. She says Greig refuses, on principle.

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Catherine Greig and Whitey Bulger (FBI File image)

Catherine Greig and Whitey Bulger (FBI File image)

“I think she has no regret. She wanted to be with him. She was with him. She had a wonderful 16 years. Wonderful,” she said, referring to their life on the lam before agents finally moved in on Bulger in the couple’s California apartment.

“This is very difficult for me because it’s my twin sister, and she has to do what she has to do, even if I don’t agree with it,” said McCusker. “She doesn’t regret it. If she did, she’d be talking now.”

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She said Greig still believes Bulger, who was convicted in 11 murders, is innocent.

Christina Hager