What matters more to Ms. Bigelow and Mr. Boal than plot twists or surprises — and to an audience torn between the urge to lean in and the desire to look away — is the minute-by-minute unspooling of accident, error and intentional evil that produced a tragic result. The important thing is not the literal accuracy of the overall account (though Mr. Boal, a former journalist, has been diligent in his research) but its plausibility. Is this what could have happened? Does it feel true?

The answers, of course, can hardly be objective. The language of cinematic action — which Ms. Bigelow speaks as fluently and inventively as any living American director — is an idiom of feeling and visceral response. There are parts of “Detroit” that have a raw, unsettled authenticity, and others that sink in a welter of screaming and cursing.

The Algiers becomes a trap, not only for the characters, who are stuck inside at the mercy of a maniac, but for the film itself, which loses its political and psychological coherence as the night drags on. Krauss, with his disconcertingly boyish looks and his sophomoric attempts to seem thoughtful, is a callow sociopath. His fellow officers Flynn (Ben O’Toole) and Demens (Jack Reynor) contribute sexual hysteria (when they see white women in the company of black men) and sheer idiocy. They are terrifying and contemptible — dismayingly believable figures from the prehistory of what is now called the alt-right.

But as their villainy comes into relief, the humanity of their hostages begins to blur. In a horror movie, the monster is inevitably the center of interest, and once the first body in the motel falls, “Detroit” begins to trade its vivid sense of nuance — especially present in its delicate observation of Fred and Larry’s friendship — for bluntness and sensationalism. A complex, dreadful piece of history becomes an undialectical ordeal of viciousness and victimhood.

The film opens with the assertion that in Detroit and elsewhere in the mid-1960s, “change had to come” and “the question was when and how.” But the promise implied in that “how” is one that “Detroit,” for all its impressive craft and unimpeachable intention, proves unable to fulfill. It is curious that a movie set against a backdrop of black resistance and rebellion — however inchoate and self-destructive its expression may have been — should become a tale of black helplessness and passivity. The white men, the decent ones as much as the brutes, have the answers, the power, the agency.

The filmmakers seem aware of this problem. They try toward the end to give the movie back, in effect, to its African-American characters, to refuse to let racism have the final word and to free themselves of storytelling conventions that insist on comfort and consensus. It doesn’t quite work. American movies have a hard time with division and with real-world problems that have yet to be solved. American politics does, too. The great virtue of “Detroit” is that it recognizes this difficulty. The failure to overcome it is hardly the film’s alone.