A Mighty Heart chronicles Mariane's search for her husband, a Wall Street Journal reporter, who was abducted by terrorists and killed in Pakistan in 2002.
And the former Friends star had been discussing taking on the role when she helped Pitt acquire the movie rights to Mariane's book.
"It was Jen who persuaded Daniel Pearl's wife to sell their production company Plan B the movie rights.
"It is heartless but the bottom line is Brad got ownership of the company in their divorce settlement, so he can do what he likes."
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