I had loosely heard of the West Memphis Three for years, but only now do I understand the full story. I'd say that Atom Egoyan is the proper director, since he specializes in grim topics (a school bus crash, the Armenian Genocide, etc). The preacher's claim that satanic music caused the defendants to commit the murders sounds like the typical stuff that we hear from religious nuts. As for the movie's focus on Stevie Branch's family as opposed to all three families, it was most likely because they cast Reese Witherspoon as the mother.
The movie ends by noting what happened in the years after the trial ended. What's most intriguing is that the man who came into Bojangles's and was never seen again. What secrets do all the people in West Memphis hide? Whatever the case, this sounds like one horrifying event. "Devil's Knot" is not a great movie, but I recommend it. Also starring Colin Firth, Mireille Enos, Alessandro Nivola and Bruce Greenwood.