It’s been nearly 19 years since the bodies of three 8-year-old boys were discovered naked and bound in the woods near their homes in West Memphis, Ark. A month after the killings, three teenage boys were charged with the murders (amid rumors of rape, mutilation, Satan worship and — horrors — an interest in heavy-metal music). Within a year, the young men had been convicted. One of them was sentenced to death.

But I’ll bet you already know this. The circumstances and bizarre carriage of justice that swirled around the “West Memphis Three” prisoners became the stuff of outsider outrage when Joe Berlinger and Bruce Sinofsky’s first documentary about the murders, “Paradise Lost: The Child Murders at Robin Hood Hills,” aired on HBO in 1996.

A sequel, “Paradise Lost 2: Revelations” followed in 2000; together, both films made an increasingly compelling case that Damien Echols, Jason Baldwin and Jessie Misskelley had been wrongly tried on shoddy evidence. Moreover, the films told a deeply disturbing and apparently unforgettable story about human nature, grief and mob vengeance — effectively turning the West Memphis events into a modern-day analogue to the Salem witch trials. The “Paradise Lost” films became, for lack of a better description, a cult hit.

In their riveting “Paradise Lost 3: Purgatory,” premiering Thursday night on HBO, Berlinger and Sinofsky return to West Memphis to finish what has undeniably become a life’s work. Another decade has passed. The teens have aged in prison, now approaching their 40s, while appeal after appeal was denied by the judge who oversaw their trial.

“Paradise Lost 3” is perhaps the most interesting and well-made film of the trilogy, not only because of its mixed-blessing epilogue, in which Echols, Baldwin and Misskelleywere freed from prison with an Alford plea deal last August. Agreeing to the plea technically released them, but it left the case unsolved.

The film ruminates in many morose ways on the passage of time and the perniciousness of set minds while acknowledging the first two films’ role in bringing attention to the case. Had it not been for “Paradise Lost,” the plight of the West Memphis Three might never have become a celebrity cause, attracting the moral and financial support of Johnny Depp and Pearl Jam’s Eddie Vedder, among others, as well as the determined work of high-priced defense attorneys and legal experts.

Indeed, the case continues to pique interest; another documentary from a different director, produced by “Lord of the Rings” director Peter Jackson, is coming soon, claiming to have details unexplored by “Paradise Lost.” The case has become a symbol, resonating with anyone who grew up in a small town and liked to wear black clothing or who felt ostracized.

Nearly everything has changed since 1993. Of the murdered boys’ parents and stepparents, one mother has died. A father whose hatred for the accused was so memorably aflame in the first film has completely changed his mind and now publicly proclaims the men’s innocence. The attention from the documentaries and celebrity influence has soured local perceptions of the facts in the case. Though it seeks to right a series of wrongs, “Paradise Lost” remains a fascinating study in the power of media and suggestion.

And what of those poor little boys? (Caution: “Paradise Lost 3” unflinchingly provides police footage of the crime scene.) Who killed them? The film turns its attention to claims of DNA evidence that links one boy’s stepfather to the crime — a claim repeated at a rally by Dixie Chicks singer Natalie Maines. The stepfather, Terry Hobbs, sued Maines for defamation, which may have been a miscalculation on his part: His videotaped deposition by Maines’s attorney opens a door from which a forgotten chill blows in, renewing a viewer’s fascination once more. Hobbs, who is interviewed in the film, has denied having any part in the killings.

Though “Paradise Lost 3” bills itself as a conclusive chapter and exults in freedom for the West Memphis Three, it feels as though we haven’t yet made our last trip to those haunted woods.

Paradise Lost 3: Purgatory

(122 minutes) airs Thursday at 9 p.m.
on HBO.