Detroit John Boyega, Will Poulter, Algee Smith. Directed by Kathryn Bigelow. Rated R. Opens Friday citywide.

The third collaboration between director Kathryn Bigelow and screenwriter Mark Boal, Detroit is less focused and powerful than their previous two films (The Hurt Locker and Zero Dark Thirty), although it’s no less meticulously researched, with moments of great impact. Set mostly during the Detroit riots of 1967, the movie begins with a clumsy animated montage giving a truncated history lesson about African-American migration to northern industrial cities and white migration to the suburbs. That dull, educational tone doesn’t extend to the rest of the movie, which aims to put viewers alongside the black residents of Detroit as they rebel against police brutality and economic inequality.

For the first 40 minutes or so, the story checks in with a range of characters, first showing the inciting incident of the riots (a raid at an illegal after-hours club), then moving through growing violence and an appeal by Congressman John Conyers to stop the destruction. Eventually Bigelow and Boal focus the movie on a single notorious event, the murders of three young men at the Algiers Motel on the third night of the riots. The movie spends more than an hour on this tense standoff, as a group of local cops led by the sadistic, unhinged Officer Krauss (Will Poulter) rounds up and torments several black men and two white women after suspecting one of them of shooting at the police.

John Boyega brings dignity and quiet authority to his performance as Melvin Dismukes, a black security guard caught in the middle of the investigation, but Poulter turns Krauss (a fictionalized composite of real officers) into a cartoonish horror-movie villain, and a movie that could have been about a spectrum of people affected by systemic injustice turns into a thriller about one absurdly evil guy abusing his authority. The Algiers section of the movie is harrowing in its own way, and might have worked as an entire film to itself. But with all of the drama leading up to it, plus half an hour of incidents afterward (including a trial that took place two years later), it ends up dragging the narrative down rather than giving it a purpose.

There’s still some touching character work in the margins, including from Algee Smith as aspiring singer Larry Reed, whose dreams don’t survive the trauma of his experience during the riots, and from Anthony Mackie as a Vietnam veteran disgusted by the war zone he finds upon returning home. Cinematographer Barry Ackroyd gives the movie a visceral immediacy, putting viewers in the middle of the chaos and violence. The movie’s structure isn’t nearly as effective.