Collaborating with Jackson and his partner, Fran Walsh, were Damien Echols and his wife, Lorri Davis, as producers. The documentary was directed by Amy Berg ("Deliver Us From Evil"). The executive producer is Jackson's longtime manager, Ken Kamins, who is repping the film's sales.
As to how long the documentary was in production or how it came to be is, according to a release announcing the project, is much of the film itself.
The release opens with a statement from Echols, with a dateline of Wellington, New Zealand November 2011:
“It is our hope that this film will help educate people about how badly the justice system can fail us all – but beyond that, we want to show that in the face of such horror, in the face of resounding grief and pain, you cannot give up… you must never give up.”
Of course, there is another film -- three, in fact -- that have already been made around this case and those emotions: Joe Berlinger and Bruce Sinofsky's "Paradise Lost" franchise, which was produced in association with HBO.
The most recent, "Paradise Lost 3: Purgatory" premiered at the Toronto Film Festival with its original ending and again at the New York Film Festival with the new ending that showed the men being freed in August after taking an Alford Plea. That film is on the shortlist for the best documentary Academy Award; there's also been discussion of the possible fourth installment.
The release quotes Echols as saying Jackson and Walsh suggested making "West of Memphis" more than three years ago. ("Paradise Lost 2: Revelations" was released in 2000; "Paradise Lost 3" will premiere on HBO in January.)
“September 2008 was one of my lowest points. Judge David Burnett had refused to hear any new evidence - this included new DNA testing... as if proof of our innocence was somehow irrelevant. I thought we had come to the end of the line, that there was nowhere else to go. It was at this point that Fran and Peter suggested that maybe there was another way of fighting back... that if the evidence was not going to be allowed to be heard in a court of law, it would be heard in another forum. That was when they said to me and Lorri, ‘We should make a film’.”
Jackson and Walsh worked with the WM3 for five years, financing research that would prove their innocence. (Jackson's involvement with the case was not made public until after they were freed from prison.)
Berg's film is said to contain "forensic evidence... that uncovered startling new findings pointing to the innocence of Echols, [Jason] Baldwin and [Jessie] Misskelley Jr. and includes new forensic evidence that points to other suspects that the West Memphis police chose to overlook. It was this new evidence as highlighted in the documentary that ultimately prompted the Arkansas Supreme Court to overturn previous denials of appeals and allowed for a new evidentiary hearing to proceed."
Atom Egoyan is also developing a feature based on the case, "Devil's Knot."