Oddly in sync with the narrative strategy (though without the imposing visual panache) of “Dunkirk,” the other historical drama of the moment, director Kathryn Bigelow’s “Detroit,” is an artfully frazzled mosaic of suffering, putting the audience through the wringer in the name of truth, injustice and what many see, still, as the American way with police brutality.

In various, depressing ways, the film speaks to our present-day rage-fueled American divisions, clear echoes of where we were 50 years ago. Audiences are responding to “Dunkirk” because it’s a reassuring period piece, about grace under pressure and never giving up. “Detroit” is a tougher sell for a Friday night at the movies, because it’s about people who never had a chance at justice in the first place.

On July 23, 1967, police raided an illegal after-hours bar (a “blind pig”) on Detroit’s Near West Side. This sparked riots that, as one character in the film notes, exceeded the destruction of the 1943 Detroit clashes between police and African-American citizens. In the movie, Anthony Mackie plays a key supporting character, real-life Vietnam War veteran Robert Greene, caught up in the blind pig raid and the ensuing nightmare. He later described it as worse than anything he endured in Vietnam.

Some characters are pulled from the historical record; the key fictionalized character (for legal reasons), a venal, sociopathic police officer played by Will Poulter, is based on an officer found not guilty in court by an all-white jury. The excruciating centerpiece of “Detroit” concerns what happened at the Algiers Motel, an $11-a-night dive, home to hookers and johns and all kinds of transients. A group of officers, mistaking a starter’s pistol for sniper fire, turned against innocent suspects in a show of outlandish, illegal force.

It’s one hell of a difficult sequence to endure. Bigelow does not elide or cut out anything for the sake of going easy on the audience. The film’s audience surrogate, who remains watchful on the margins of this long scene, is real-life security guard Melvin Dismukes, played by John Boyega of “Star Wars: The Force Awakens.” He’s a singular note of decency amid an indecently cruel scenario.

But Poulter is miscast, and one-note, and it seriously hurts “Detroit.” As written and as acted, the vicious cop here called Krauss (whom we first see shooting a looter in the back) serves as the embodiment of all law enforcement evil, a scared, racist, paranoid bully acting with impunity, pulling his partners (one willing, the other reluctant) into the escalating carnage.

The casting, for the most part, seamlessly mixes relative newcomers with seasoned pros. The movie interpolates archival footage (Michigan Gov. George Romney decrying “hoodlumism”) indicated by a narrow aspect ratio. “Change was inevitable,” one title card reads in the animated “Detroit” opener, using illustrator Jacob Lawrence’s paintings. It’s a disarmingly folkloric way to introduce the blood-stained mosaic to come.

I watched “Detroit” with one eye on a movie yet to be made. If anyone is ever to take on a major piece of cinematic historical fiction dealing with Chicago in August 1968, Bigelow’s “Detroit” offers intriguing signposts about what might, and might not, work. A handful of films, from “The Battle of Algiers” to Paul Greengrass’ splendid “Bloody Sunday,” have met the challenge of dramatizing civil unrest and law enforcement outrages, memorably. “Detroit” comes close.

MOVIE REVIEW

“Detroit”

Grade: C+

Starring John Boyega, Jacob Latimore and Will Poulter. Directed by Kathryn Bigelow.

Rated R for strong violence and pervasive language. Check listings for theaters. 2 hours, 23 minutes.

Bottom line: Comes close to meeting the challenge of dramatizing civil unrest