The notorious case of the West Memphis Three, the trio of lower-class teenagers who were charged with killing three young boys in 1993 in West Memphis, Arkansas—supposedly as part of their Satanic rituals—has been the subject of multiple documentaries, most notably the HBO trilogy of “Paradise Lost” films made between 1996 and 2011 and the 2012 documentary “West of Memphis,” which also covered their release as the result of a curious plea deal. Now Atom Egoyan has directed this docu-drama about the case, concentrating on the initial trials that resulted in the youths’ convictions and only sketching later events in text cards at the close.

It’s not difficult to understand why Egoyan might have been attracted to this material. Thematically the story he chooses to tell, concentrating on the grief and guilt that surrounds the boys’ murders, is related to his masterly 1997 adaptation of Russell Banks’ “The Sweet Hereafter.” And he sporadically captures a similar sense of loss here, as in the haunting sequence in which the dead boys’ bodies are lifted from the creek in which they’re found and tenderly placed on the bank.

Otherwise, however, “Devil’s Knot” fails to achieve an equal measure of emotional power. The earlier film centered on Ian Holm as a lawyer attempting to enlist the parents of children who were killed in a school bus crash in a court action; this one focuses on private investigator Ronald Lax (Colin Firth), who offered his help to defense lawyers and, at least in this telling, developed most of the leads that cast serious doubt on the prosecution’s case, and on Pam Hobbs (Reese Witherspoon), the mother of Stevie Branch (Jet Jurgensmeyer), one of the victims, whose relationship with her husband Terry (Alessandro Nivola) grows strained as the ordeal continues. (Hobbs, of course, has more recently emerged as a prime suspect in the killings.) Unfortunately, neither character catches fire here, and the concentration on them shunts the three accused teens—Damien Echols (James Hamrick), Jessie Misskelley (Kris Higgins) and Jason Baldwin (Seth Meriwether)—curiously into the background. Even Lax’s ex-wife (Amy Ryan), who’s harassed by the cops, gets more attention than they do—as does another early suspect Chris Morgan (Dane DeHaan), whose over-the-top behavior when interrogated b the police was certainly grounds for a closer look.

The major thrust of the script that Paul Harris Boardman and Scott Derrickson adapted from Mara Leveritt’s book is that the police and prosecutors created a case virtually out of whole cloth, using a woman who might be prosecuted for other crimes (Mireille Enos) and her pliable young son (Jack Coughlan) to provide damning evidence and dubious experts like Echols’ parole officer (Elias Koteas) to expound sensationalist theories on the stand while the judge (Bruce Greenwood) allowed such tainted testimony into the record while systematically excluding exculpatory evidence. The trials are presented very much as a rush to judgment explained by the desire of public officials to placate public outrage, represented by the infamous rants of John Mark Byers (Kevin Durand), stepfather of another of the murdered boys, who for a time was thought to be the prime alternate suspect until the emergence of evidence against Hobbs.

There’s no longer much question that the original convictions of the West Memphis three represented a judicial travesty, capped by the logically absurd plea bargain that allowed a trio of young men the state still officially considers guilty to go free. But while Egoyan’s stately, somber (and starry) take on the early stages of the story is certainly an earnest effort to portray the miscarriage of justice that occurred in 1993-94, and as such can bring the cautionary tale to viewers who might not be familiar with the case already, the fact is that it doesn’t differ very much from a good television real-life adaptation. Part of the problem, to tell the truth, lies in the performance of Firth, whose general passivity makes Lax an oddly drab protagonist. In fact, no one in the cast—including Witherspoon—proves much more than adequate.

Technically the film is proficient but not outstanding, with Paul Sarossy’s cinematography reaching eloquence only occasionally, as in the body-recovery sequence. On the other hand, Mychael Danna contributes a moody score that adds some of the atmosphere the picture as a whole lacks.

Newcomers to the story of the West Memphis Three will find “Devil’s Knot” an honorable if muted attempt to portray a case that was a tragedy in more than one sense; those who have seen the previous documentaries won’t find much in Egoyan’s film they don’t already know but may be interested in seeing the tale told from a slightly different perspective. But coming from such a talented filmmaker, the film is disappointingly prosaic, unable to shake a Lifetime movie-of-the-week quality.