To neighbors and casual acquaintances, they always seem to have come across as loners, quiet types who kept to themselves. Were they depressed? Lonely? Or just burning with rage? Nobody can say for sure, but campus gunmen who open fire on their classmates remain frustratingly enigmatic to an obsessed public searching for motives.

In the wake of such carnage, our hearts go out to the victims and their families, but how do we respond to the parents of the perpetrator? Do we acknowledge their loss, and pity them for their unexpected brush with infamy? Or do we blame them for raising a monster?

Beautiful Boy is the story of two such parents, whose 18-year-old son Sam (Kyle Gallner, of last year’s A Nightmare on Elm Street) orchestrates a campus massacre before turning the gun on himself.

Bill (Michael Sheen), his emotionally distant father, avoids the subject at first. Rather than confront his role in creating a killer, he throws himself into his workouts, then runs off to bed. He addresses mundane concerns, issuing a statement to the media, paying off his son’s student loans, even making overtures to his boss about returning to work. He keeps the devastation at bay as long as his sanity will allow, but even Bill, aloof as he seems, has a breaking point.

In some ways, Kate (Maria Bello) has already reached that point. Even before the killings, we get a taste of her desperation. Planning a vacation as a means of reaching out to her estranged husband and son, she is hungry to fix a family that no longer works. She and Bill go through the motions, but their lives are governed by lifeless routine.

Where did it all go wrong? What could they have done differently? Bill and Kate struggle with these questions as denial gives way to heavy-hearted acceptance, and to his credit, writer-director Shawn Ku doesn’t offer any easy answers. A plaintive response to the 2007 shootings at Virginia Tech, where Ku's parents met and married, Boy gives us an unflinching glimpse into the lives of parents who can never reconcile themselves with the sins of their son, much less understand them.

“Good people sometimes do bad things by mistake,” Kate tells her young nephew, who sees his cousin on TV but doesn’t quite grasp why he’s there. It’s a trite sentiment, a meager defense for a terrible act, but what else is she to say? Bill and Kate take turns venting their anger at each other before reluctantly looking in the mirror, but at the end of the day how much responsibility should they assume?

A perfect companion piece to Gus Van Sant’s Elephant (2003), which followed like a ticking clock the events leading up to a high-school atrocity, Boy is unrelentingly somber, a raw portrait of pain from which there is no escape and only the briefest of respites. (Almost defiantly, Bill and Kate reignite their sex lives one night over a drunken game of poker.)

Some viewers will see this as a one-note film, morbidly fascinated with our own morbid curiosity, about a couple thrust into the public eye under the most ghoulish circumstances, vilified for a crime they didn’t commit and barely comprehend. Yet Boy, for all its exploitation of the sensational, is a tense affair that challenges us with questions we may never have thought to ask.

Anchored by the powerful performances of its stars, who hold us rapt but never overplay their anguish, it is a two-hour plunge into the depths of human despair. What we find there is at once ugly, disturbing and, in the end, curiously hopeful, but even at its darkest, Ku’s vision is compelling and painfully authentic.