If you’ve seen the “Paradise Lost” trilogy on the case, “West of Memphis” will be a must. If not, it’s even more so. The travesty of justice that the 1994 conviction of three young men in small-town Arkansas for the brutal murders of three eight-year old boys represented was first taken up cinematically by documentarians Joe Berlinger and Bruce Sinofsky in the initial HBO installment of their trilogy, which gave birth to a grass-roots campaign to have the case reopened and the convictions reversed. The film and its sequels are the most significant, and effective, cinematic assault on the American justice system since Errol Morris was instrumental in freeing a wrongly-convicted man from the Texas death row with “The Thin Blue Line” in 1988.

Among the supporters that Berlinger and Sinofsky’s investigations attracted to the cause of Damien Echols, Jason Baldwin and Jessie Misskelley, Jr. were Peter Jackson and Fran Walsh, who, along with Echols, who was released after some seventeen years awaiting execution, produced this recap of the entire case, directed by Amy Berg and co-written by her with Billy McMillan. It repeats a good deal of the content of the “Paradise Lost” series, which was completed only this year with the third and final installment, and viewers familiar with those three films will mostly find themselves reacquainting themselves with the case rather than learning new facts about it. What’s made abundantly clear is the dedication of supporters in collecting evidence that threw doubt on the convictions and the abject failure of the Arkansas courts to show any willingness to hear it.

The one major new thrust, which was certainly touched upon in “Paradise Lost 3” but considerably expanded on by Berg, is the argument that the stepfather of one of the victims might have been the actual perpetrator. Not John Mark Byers, the hot-tempered stepfather of Christopher Byers, who was identified as a suspect in “Paradise Lost” 2, but Terry Hobbs, the stepfather of Stevie Branch. Substantial evidence is amassed here against Hobbs, not only in terms of information about his past life and holes in his alibi—matter discussed briefly by Berlinger and Sinofsky after Hobbs unwisely left himself open to questioning under oath by bringing suit against the Dixie Chicks, who were vocal supporters of the convicted men—but new data including DNA findings and indirect testimony from friends of Hobbs’s nephew that the family was aware of his guilt.

To be sure, it’s doubtful that the information assembled against Hobbs would be sufficient to convict him of the murders, and in that respect one might accuse Berg—whose presentation is, frankly, pretty aggressive—of espousing the same attitude of presumption of guilt against him that prosecutors, the media and the public took against Echols, Baldwin and Misskelley. But one’s sense of disquiet over that has to be mitigated by the totally unsatisfying and illogical outcome of the Arkansas legal process, which in 2011 employed a little-known provision of the law called an Alford plea, by which the three were released after agreeing to present a guilty plea while still maintaining their innocence. The arrangement effectively means that the state considers the case closed while returning to society men whom it still legally considers responsible for a heinous crime (one of whom had been sentenced to death), effectively precluding any official investigation of the person who might actually have committed the act.

In any event “West of Memphis” is primarily important for shining a spotlight on one of the most egregious miscarriages of justice in recent American history, and doing so in the form of a single, comprehensive film (though a long one at 2½ hours) that some might be more willing to watch that three very long documentaries. And by including a wealth of new interviews with the accused, their families, lawyers and advocates (most notably Echols and his wife Lorri Davis, who helped spearhead the effort on their behalf), the victims’ relatives, prosecutors, judges and others (including the two young men who report on what Hobbs’s nephew said), as well as offering post-prison portraits of the three released (if not officially exonerated) men, it gives some indication of the enormous human cost of the entire unhappy episode.

Still, it should never replace the “Paradise Lost” trilogy, which stands beside Morris’ groundbreaking work among the milestones in activist American non-fiction filmmaking.