The lawsuit and Mr. Hernandez’s case proceed against a backdrop of higher-profile public events like the killing of Eric Garner, the scandals that thinned the upper ranks of the police and the release of the United States Justice Department’s Ferguson Report, which highlighted the way that city in Missouri used fines and penalties as a source of revenue and made its police into armed tax collectors preying mostly on nonwhite citizens. “Crime+Punishment” advances a thorough critique of American law enforcement not by generalizing or speechifying, but by digging into particular lives and circumstances, allowing affected individuals to speak for themselves.

The result is a powerful and suspenseful film, part detective story and part courtroom drama, fueled by a potent mix of curiosity and indignation and full of memorable characters speaking in the lively idioms and varied accents of New York. Mr. Maing brings viewers into the daily lives of police officers, some of them veterans with decades of service behind them, who are willing to risk their careers for what they believe is right. They face fear, frustration and agonizing uncertainty as the case proceeds.

If “Crime+Punishment” were a scripted feature rather than a documentary, it would have a neater, and perhaps more unequivocally hopeful ending. You can extract a degree of optimism. Sometimes justice prevails. Sometimes politicians and judges listen. But never automatically, through the impersonal workings of the system. This film is about the work, risk and sacrifice — the combination of stubbornness, courage and decency — required to make the ideal of equal justice under the law anything close to a reality.