Filmmaker Atom Egoyan once seemed a Canadian on the cusp of the canonic (Exotica, The Sweet Hereafter). But Devil’s Knot takes a cracking true-life tale and cracks it to pieces. Why even make a dramatised version of the West Memphis killings, those triple-homicide child murders with subsequent travesties of justice that have inspired four documentaries to date? A bemused Colin Firth, playing a private eye, wanders about with a bemused Arkansas accent. Reese Witherspoon is better, but not film-savingly, as a bereaved mum. The whole thing is ill-scripted, ill-directed and, worst of all, superfluous.