They say there’s nothing more painful than losing a child, but what about losing your child when he kills 20 people and then himself in a collegiate shooting rampage? This harsh chamber drama by first-time filmmaker Shawn Ku focuses tightly on a professional couple (Maria Bello and Michael Sheen, both excellent) who are thrust into a nightmare when their morose only child goes berserk during his freshman year. Despite the fact that this sort of tragedy has become commonplace in America, the emotional experience of being the monster’s mom and dad is still uncharted territory, and Ku handles it credibly, rooting his cramped, near-surreal story in the practical details of dealing with the police, making a public statement, grieving appropriately, and trying to escape the media circus. The most daring aspect of the film, fully realized in Bello’s grave performance, may be the notion that a parent can invest endless love in a child and one day find him unfathomable. R, 100 min. River East 21