In any era of systemic corruption and malpractice, whistleblowers naturally emerge. But rarely do we get to see the human face behind their mettle, let alone the toll it takes on the psyche to be a cog in the machine of a system they know to be unjust. That’s what film-maker Stephen Maing achieves with Crime + Punishment, his new documentary about the 12 cops, all people of color, who fought back against the New York police department’s covert and illegal quota system, which led to a class action against the department over its practice of pressuring minority officers to issue predetermined numbers of arrests and summonses per month – oftentimes in communities of color deemed “high-crime”.

The documentary opens in the tradition of investigative cinema, with a clandestine phone conversation between Maing and Sandy Gonzalez, a 12-year veteran and the first of the dozen officer mutineers. “They’re retaliating against me because of my numbers,” says Gonzalez, who would eventually be demoted after resisting his supervisor’s demands. We’re then thrown in the middle of the police academy graduation, where New York, New York plays and then police commissioner Bill Bratton waxes poetic about the city having “reclaimed its streets”.

Bratton, widely considered the architect of the broken windows theory that leads to the aggressive policing of minority communities by zeroing in on so-called “minor crimes”, can be seen in the documentary insisting that the NYPD targets behavior, not communities of color. But the footage and audio Maing compiles – often shot from a purposeful distance, and much of which consists of stealthily recorded conversations between the NYPD12 and their supervisors – suggest otherwise.

“This is a story we didn’t ask permission from the department to make,” says Maing, who previously worked on several short and mid-length documentaries about policing in New York before making Crime + Punishment. “There were situations and experiences that we knew the public would never believe if they couldn’t see it firsthand. So if I placed myself very judiciously in a couple different places in the film, there could be this signaling that I and the audience are newcomers to some of these situations.”

The result is an extraordinarily panoramic and yet granular view of the criminal justice system in New York City, emphasized by the juxtaposition of broad, skyline shots with rickety, undercover camerawork. At times, Crime + Punishment proceeds like cinema vérité; at others, like a tightly constructed exposé. Most impressive is the level of access Maing manages to procure. Large chunks of the film are spent with the whistleblowing cops, like Gonzalez, Edwin Raymond and Felicia Whiteley, but also with the lawyers and private investigators working with the young men most directly affected by the quota system.

“At a certain point during filming it became clear to me that if we weren’t able to show the collateral damage, the very human experience of people on the receiving end of over-policing in minority communities, that we wouldn’t be able to convey the urgency of this,” says Maing, who after four years of shooting had over 1,000 hours of footage. “The thing that can never be lost is that these are real cops, real families, real young men spending months or years in Rikers doing real time for real charges that may not be passing the burden of proof or sufficient probable cause.”

One of those young men is Pedro Hernandez, a Bronx teen jailed in Rikers over gun possession and assault charges that were later dropped. In one memorable shot that gets the blood boiling, his mother leafs through pages and pages of dismissed charges. Hernandez’s case was picked up by private investigator Manny Gomez, a cop-turned-defector whose investigations have led to the dismissal of nearly 100 charges. Intrepid and burly, he’s one in a cast of dogged figures Maing followed between 2014 and 2017, earning their trust as the NYPD12 grew in both strength and numbers.

The unofficial flag-bearer for the class action filed against the department would be Raymond, shown in one scene recording a conversation with his supervisor, who not-so-coyly suggests Raymond’s failure to earn a promotion has to do with him being a “loud” black man with “dreads”. At one point in the documentary, he puts the injustice of the quota system in powerfully succinct terms: “The reality,” he says, “is that law enforcement uses black bodies to generate revenue.” The implications of such institutional malpractice are far-reaching, given that the policies of the NYPD, the country’s largest and most well-known police force, are replicated nationwide.

“There are many departments that reference the NYPD patrol guide and, in some cases, their policies verbatim,” says Maing, referring to the way broken windows policing has been adapted in places like Ferguson, where Michael Brown’s death set in motion the Black Lives Matter movement. “We have to have a very mindful conversation about whether these practices and tools are bolstering trust within the community of policing. Does it maintain and grow the respect of the uniform in communities of color? The idea that police have lost respect and legitimacy as a result of practices that fray the social contract between them and minority communities is alarming.”

As his documentary has toured the film festival circuit, Maing has been approached by a number of law enforcement officers who complain of similar policies enacted in their own departments. It has shown him that issues of policing and race don’t fall neatly into the binary structures by which much of our political discourse has been subsumed.

“What’s really exciting to me about this project is that this is a voice we haven’t heard yet,” he says. “It doesn’t fit into that divide of hopelessly progressive, anti-police liberals and hopelessly blinded conservatives who are pro law-enforcement at any cost.”

In foregrounding the psychological and physical impact of being forced, as Raymond says, “to participate in something that disenfranchises black folks even more”, Maing has made a documentary that’s less concerned with politics than basic ethics. Not only have the NYPD’s policies transcended our conventional notion of liberal versus conservative approaches to policing – the events shown in the documentary take place under Bill de Blasio’s administration – but the renegade cops who take on the system do so out of an earnest desire to reform, not dismantle, the department.

“Crime is a reality and we need police,” says Maing. “This is not just about disgruntled cops who have a bone to pick or want to be famous and make money. They’re cops who believe in the mission of policing itself.”

The enraging, incendiary and expertly crafted Crime + Punishment arrives in a moment inhospitable to the nuanced conversations required of the topic. It is harder than ever, says the director, to cut through the breakneck cycle of Washington DC headline news, from the president’s tweets to the latest secret Omarosa recording. But in a country that was already splintered over issues of race and policing, the moral, social and legislative gravity of the film is made more explicit.

“After this film, I’ve heard so many people say, ‘If something were to happen to me, I don’t know if I want to call the cops because I’m fearful of what could go wrong as a black person,’” Maing recalls. “It’s become harder to have a rational and calm conversation around what works and doesn’t work in policing. Maybe for that reason, this was an opportune time to do a deep dive into this story.”

• Crime + Punishment will be available on Hulu from 24 August with a UK date to be announced