Mexican director Alejandro González Iñárritu aims to repeat last year’s success and become the first director to collect consecutive Oscars since Joseph L. Mankiewicz in 1950. Yet Iñárritu’s revenge tale The Revenant, has nothing to do with Mexico, unlike another nominated film.

U.S. director Matthew Heineman’s Cartel Land – up for Best Documentary – provides an engrossing glimpse into Mexico’s violent drug cartels.

It tells the parallel stories of two vigilantes on both sides of the border – in Arizona and the crime-ravaged Mexican state of Michoacan.

The extraordinary access Heineman obtained to the Mexican vigilantes, or autodefensas, is apparent from the opening, where we bear witness to what looks like a pagan ritual in a forest. Yet the masked man shrouded in circling wisps of smoke is not a medicine man but a meth cook, and he explains his motives in a hushed, confessional tone.

Much has been made in the media of this unprecedented access. Later, there are even extremely disturbing scenes of shootouts and torture rooms.

But the film does not rely solely on its insight into the politics of vigilantism. The director also gains extraordinary personal access to the movement’s leader, Dr José Manuel Mireles.

Heineman was introduced to the film’s central subject by a journalist who said he was the “most interesting man” she knew.

The film certainly bears this out. Mireles is a captivating presence: commanding, yet soft-spoken and sympathetic. But this is no whitewashed portrayal. We also see his shortcomings and transgressions, which range from cheating on his wife, to ordering an execution.

The documentary traces this charismatic leader’s rise and crashing fall. By the end, he is an isolated figure, in conflict with old friends and in fear of reprisals.

Sadly, the film has a glaring flaw. The Arizona scenes are neither revealing nor captivating. The “heavily armed drug smugglers and human traffickers” that we are warned about at the beginning never make an appearance. Instead, a self-appointed border agent apprehends a group of unarmed migrants hiding in a bush.

The story in Michoacan drowns out Arizona, creating an imbalance that detracts from the film.

Yet as events south of the border go into tailspin, Heineman can be forgiven for focusing on Mexico.

By the end of the film, we have come full circle. We are back in the forest, among the smoke and the meth. The gangs have been chased out, but what has replaced them? “Someway, somehow, everybody has gotten corrupted,” the masked man reveals. “The autodefensas and the people cooking meth, we’re pretty much the same team.”

Cartel Land is available on Netflix in Mexico and the United States.

Twitter: @Stephentwoodman