The infamous filmmaker finished editing "The Ghost," which features the Irish actor as a British prime minister accused of war crimes, the day he was arrested.
Now Robert Harris, the writer of the screenplay, says that Polanksi is putting finishing touches on the film while behind bars facing extradition to the U.S. to be sentenced for having sex with a 13-year-old girl in 1977.
"He can make his wishes known from his cell -- whether the film can rise above the circumstances in which the director finds himself I don't know," Harris told the Times of London.
"We will test to the upper limits the notions that there's no such thing as bad publicity."
"The Ghost," which co-stars Ewan McGregor and Kim Catrell, is based on an adaptation of Harris' bestselling novel that centers on a ghostwriter hired to complete the memoirs of a former British prime minister who is the target of a war crimes indictment.
The film, which is rumored to be Polanski's last, is scheduled for a February 2010 screening at the Berlin Film Festival.
To see stills from the movie, and a short trailer which looks fascinating, visit the film's Web site at theghost-romanpolanski.com.