A riot starts like a spark burning slowly down the wick of a bomb. It moves along in stops and starts, anxiety building, and unless the wick is cut, the tension skillfully de-escalated, the bomb explodes.

So begins ‘Detroit,’ the third collaboration by the director Kathryn Bigelow and the writer Mark Boal, the creative team behind “The Hurt Locker” and “Zero Dark Thirty.”

Set in the violent summer of 1967, the film is viscerally timely, relentlessly grim, and rich with strong performances, but the story, which seems disinterested in offering viewers anything beyond documenting the searing injustice of this brutal chapter in American history, is undercut by shaky camera work and heavy-handed editing. ‘Detroit’ connects with viewers like a punch to the gut, but there is no exploration of why it was delivered.

‘Detroit’ is not so much about the race riots in that major American city a half century ago as it is about the events during and following a traumatic July night at the Algiers Motel, a haven for prostitutes and drug use just a stone’s throw from where the riot began. (Filming for ‘Detroit’ drenched Dorchester’s Ashmont Street in smoke and the roar of police cars, shattering the air with bullets while on scene locally last summer. The All Saint’s Church parish house was transformed into the site of the film’s central horror.)

Larry Reed (played with sensitivity by the excellent Algee Smith) is the lead singer of the soul group the Dramatics. When the rioting brings a local performance to an abrupt end, he and his friend Fred (Jacob Latimore) head to the motel and enthusiastically join in the revelry with two white girls from Ohio, Julie Ann (Hannah Murray) and Karen (Kaitlyn Dever of “Justified”) and a group of other black men, including local guy Carl (Jason Mitchell, of “Straight Outta Compton”).

Carl fires a blank from a starter pistol out the window toward a group of National Guardsmen who are warming themselves with coffee donated by the self-possessed security guard Melvin Dismukes, who is played by a phenomenal John Boyega (“Star Wars”). The fuse catches.

Fearing a sniper firing from the Algiers, a group of Detroit police, led by Philip Krauss (24-year-old British actor Will Poulter, of “The Revenant”), storms in, all of them flushed with the simmering rage of the archetypal white racist cop. Fresh from shooting an unarmed black man in the back, Krauss is on a hair-trigger, and infuriated by the idea of two white girls having sex with black men.

This episode marks the gut-wrenching center of the film, stunning the nerves as the young men and women are told to line up facing the wall. Krauss leads his officers in a sickening “death game” meant to coerce a confession and locate a gun. A policeman brings a black suspect into a room and fires a bullet into the floor, so those outside will think someone’s been shot. But twitchy trigger fingers, and an officer who finds the idea of shooting an unarmed man in cold blood to be an all-too-plausible request, leave three black men dead by night’s end, and two white females and seven black males brutally beaten.

“I need you to survive the night,” Dismukes says to one of the terrified men.

The light of day provides little relief. Cover-ups and lies lead to the policemen being exonerated by all-white juries in courts outside Detroit. Dismukes, who was only at the scene in a fruitless attempt to stave off bloodshed, is pulled into a murder investigation.

The parallels between events in the film and a modern discussion on police brutality and race relations are not subtle. A highly publicized series of police shootings involving unarmed and seemingly non-threatening black victims in recent years still deeply affects public consciousness.

Bigelow’s penchant for war movies is particularly noticeable in ‘Detroit,’ which is shot in docu-drama style with a frenetic, jittery camera’s eye focused on the proceedings to scattershot effect. The slow build to violent rioting in the opening scene melds well with the cinematographer Barry Ackroyd’s shaky lens, which leaves viewers as disoriented and nervous as the participants.

But in moments where the brutality of Krauss’s game should be enough to put an audience on edge, it seems that the creative team doesn’t quite trust the audience to be present on the scene’s merits. The camera jumps haphazardly, slamming into the wall with Anthony Mackie (“The Hurt Locker”), a paratrooper just returned from Vietnam, and vibrating painfully close to Larry Reed’s agonized and tear-damp face.

Even as Boyega’s stone-faced security guard seeps anxiety in a police scene largely without motion, the frame maintains a slight movement. The combined effect left this reviewer wondering halfway through the film if the pit in my stomach was disgust or motion sickness.

‘Detroit’ simmers with rage and heat and fear, and Bigelow’s willingness to engage with a brutal reality is admirable. She tells the story ably, horrifies the audience effectively, and makes it abundantly clear that the line between men and monsters is thin and permeable. Still, it’s hard to escape the feeling that this is a film in love with shoving brutality into the viewers’ faces without reason.

If Bigelow hoped to provoke righteous outrage, she does that exceptionally well. If she aimed to document a horrific trauma inflicted upon the black men and white women in that motel, then she pulled that off thoroughly. But if the goal of filming this unflinching misery was to provide catharsis and understanding – beyond the acknowledgement that justice for the damage done to black bodies and souls has been troublingly rare – then she has failed.

‘Detroit’ is, in its way, an uncomplicated look at police brutality, if agonizing in the telling. Krauss morphs from being a police officer recklessly indifferent to the value of black lives into the nightmarish conductor of a psychologically and physically torturous game. He is not redeemable or explicable, his assaults are overt, and therefore his role is not a referendum on anything but his own monstrosity.

Insidious, systemic racism and how it interacts with power that carries forward into the modern day is the issue at hand. And it is that aspect of ‘Detroit’ that is largely left aside in favor of instinctive outrage.