In the new film, Witherspoon will play Pam Hobbs, the mother of one of three 8-year-old boys who were brutally murdered in West Memphis, Ark., in May 1993.
Hobbs had been among those who accused Damien Echols, Jessie Misskelley and Jason Baldwin of committing the infamous murders. In November 2007, she said new evidence had changed her mind.
"Did I really believe it, no, not 100 percent that they did it," she told Jonesboro, Ark.-based KAIT-TV. "I didn't believe they were capable enough or smart enough to have committed the crime, cleaned the scene up and be guilty for it."
After spending 17 years in prison, Echols, Misskelley and Baldwin were released from prison in August as part of a plea deal.
Over the years, Eddie Vedder, Henry Rollins and other prominent musicians had raised money in support of the West Memphis Three, who had maintained their innocence all along.
Dimension acquired the rights to journalist Mara Leveritt's book “Devil’s Knot: The True Story of the West Memphis Three” in 2006, and hired Scott Derrickson and Paul Harris Boardman to write the script.
Witherspoon is represented by CAA. Her next movie, the action-comedy "This Means War," is due in theaters Feb. 17.