It’s only been four short months since the West Memphis Three were released, but already their saga seems surreal. If a screenwriter turned in the story of what happened to Damien Echols, Jason Baldwin, and Jessie Miskelley, it would be dismissed as ludicrous.

But it really happened. In 1993, three children were killed in a muddy ditch and three other children were convicted of the murders without a shred of physical evidence because the prosecutors managed to convince a hysterical jury that they were Satanists. And if it wasn’t for filmmakers Joe Berlinger and Bruce Sinofsky, this tremendous injustice would have passed without much notice. When the pair set out to make 1996’s Paradise Lost: The Child Murders at Robin Hood Hills, they thought their movie was about depraved children killing other children. But what they ended up documenting were three kids from the wrong side of the tracks getting railroaded because the cops needed scapegoats who couldn’t mount a defense. Looking back on the first movie of the trilogy, it is now evident that the filmmakers took great pains to be impartial, even though it was increasingly evident to them that the people convicted didn’t kill anybody. By the time of 1999’s Paradise Lost 2: Revelations, the movement to free the West Memphis 3—largely fueled by the original documentary—was in full force, and the filmmakers foregrounded the many doubts about the case against the imprisoned.

Paradise Lost 3: Purgatory is in many ways the strongest of this epic work of documentary filmmaking. It is certainly the most accomplished from a technical point of view, and the most complex from a film theory point of view. Much of the first half of the movie is a tour through the story so far: it leads off with graphic crime scene footage to establish the stakes and to take the viewer back to the emotional state of the prosecutors and jurors at the time of the first trial. It is also about the impact the first two movies in the series had on the real lives of the people involved. The movie’s middle passage details the results of 18 years of investigation into the murders, including the results of DNA testing that was unavailable in 1993 and recently uncovered evidence of jury misconduct.

But it's all just a windup for the endgame: the twelve minutes of the film that was added at the last minute after the deal was struck to release the West Memphis Three after eighteen years in prison are some of the most emotionally powerful documentary scenes I have ever witnessed. In particular, Jason Baldwin’s speech at the press conference after the release has stuck with me since I saw the film at last year’s Indie Memphis Film Festival. The story of the West Memphis Three is an incredible saga of injustice and redemption, and the team of Berlinger and Sinofsky, who happened to be the right people in the right place at the right time, have created a fitting and powerful end to an epic feat of documentary filmmaking.

Paradise Lost 3: Purgatory premieres tonight, January 12 2012 on HBO.