Loosely drawn from a 2004 Playboy piece about the killing of a soldier who went AWOL while on furlough from Iraq, Paul Haggis’s wildly uneven foray into the dark side of post-traumatic stress disorder focuses on parental grief, which the writer-director bravely complicates by asking what it’s like for a patriot to mourn a son with a blemished record. Elah comes packaged as a feverish murder mystery groaning beneath too many subplots and the added weight of a strained David and Goliath allegory. But once you peel away the ballast, the movie lives and breathes as a character drama with a terrific performance from Tommy Lee Jones as the G.I.’s father. It’s a vital American story, and a rare assumption of responsibility for what we ask our soldiers to do, how we ignore them when they can’t, and what happens next.