This gripping and highly detailed documentary from director Tiller Russell (Bad Boys of Summer, The Last Rites of Ransom Pride) explores the murky and dangerous world of police corruption, particularly focusing on the case of Michael Dowd, a once bright young New York City cop who in the 1980s morphed into one of the most corrupt in the department’s history, heading a ruthless criminal network that stole money and drugs while patrolling the city he swore to protect and serve.

The film starts off with footage of Dowd in the early ‘90s in a court room openly confessing his crimes before the film jumps back in time to explain just how he got there. It’s a film that grabs you from the first minute and rarely lets go, using slick editing of archive footage and photographs to talking heads interviews with some of the key people involved in a corruption plague that lasted the best part of a decade.

These include Dowd’s partner Ken Eurell, a tough but by all accounts honest cop who is assigned right out of the academy to go on patrol with Dowd despite being warned not to get in the car with him, being drawn into his increasingly law-breaking ways and becoming if not as corrupt then certainly not an innocent bystander. The film fascinatingly explores the morality of all involved, not just its central subject, and looks at logic of cop-turned-perpetrators that you never turn on a fellow cop and the effect it has when that so-called sacred rule is broken.

The cop corruption story is something cinema has explored for a long time, to good and not so good effect, and on the surface this documentary seems to be just retreading old ground with different faces. But there’s something enthralling about hearing these guys tell the story in their own words and fighting their own corners, particularly the charismatic Dowd (fresh from his resulting 14-year prison sentence) who you simply cannot turn your attention away from whenever he speaks. Even now as he is being brutally forthright about his past criminal behaviour under the guise of a police officer, you’re never quite sure where exactly he stands, whether he is truly remorseful or simply revelling in the chance to tell his side of the story.

Precinct Seven Five plays like the documentary version of a crime story that a ‘70s screenwriter might have come up with but in reality it’s quite the contrary as the often jaw-dropping story of flagrant corruption is already earmarked for a dramatized film. Whichever crime genre director the project lands at the feet of (David Ayer? Joe Carnahan? Maybe even Martin Scorsese?), they’ll have an absolute goldmine of material with which to work. As it stands, as a piece of documentary crime recounting, it’s about effective as they come.