MEXICO CITY (AP) — The documentary "Cartel Land" opens with chilling night scenes of large-scale methamphetamine cooking in rural Mexico. What viewers later learn is how such drug production became deeply intertwined with the vigilante movement that emerged in 2013 and 2014 to oust the region's main drug cartel.

New York-based director Matthew Heineman gained unprecedented access to gun-toting vigilantes in Michoacan, where those "self-defense" forces eventually drove the pseudo-religious Knights Templar cartel out of much of the western state, but wound up being infiltrated by former cartel gunmen, rival cartels and new gangs.

Led by farmers, orchard owners and small-town doctors, the movement captured the imagination of Mexicans fed up with drug violence and a government that in parts of the country is too corrupt or too inept to fight back.

"The central question I'm trying to answer in this film is whether it's just for citizens to take the law into their own hands," Heineman said at a recent news conference in Mexico City. "It's a story about what we would do if violence came to our front door."

Heineman paired the story of Michoacan with the tale of vigilantes north of the border: war veteran Tim "Nailer" Foley and his Arizona Border Recon that patrols areas of that state looking for migrants but, more importantly, drug smugglers.

It would seem like an odd coupling, but Foley expresses admiration for the Mexican vigilantes, who, like Foley, are fighting a quixotic battle against the drug cartels. "This is a war of David and Goliath, and we're David," Foley says.

But it is the Mexican vigilante movement, along with its charismatic leader, Dr. Jose Manuel Mireles, that receives the most attention. Describing the Knights Templar's reign of terror and extortion, Mireles asks, if facing a similar situation, "What would you do?"

Heineman originally planned only to tell the story of American vigilantes, he said, but after hearing about Michoacan, "the film took a complete shift and became this parallel story about citizens on both sides of the border fighting back against the cartels."

Much of it is the first time such aspects of the Michoacan movement have been captured on film, which won awards for best cinematography and best director for a U.S. documentary at the 2015 Sundance Film Festival. Heineman, a cameraman and a team of two or three people spent two weeks of each month in the field for nine months, allowing them intimate access to both the good and bad.

Feared Knights Templar gunmen are captured and turned over to police, and emboldened townspeople face down Mexican troops trying to confiscate the vigilantes' guns. But toward the close of the film, a uniformed police officer acknowledges producing drugs. Another says he is a member of a new gang, known as "Los Viagra."

The documentary is beautifully filmed, with harrowing action scenes and sound that put viewers in the middle of what they're seeing, including a torture center run by the vigilantes, where they are seen and heard abusing detained prisoners.

"I never knew who I was with — the good guys or the bad guys," Heineman said in an earlier Sundance interview.

The film, with the Academy Award-winning director Kathryn Bigelow as executive producer, opens in Mexico on Thursday, in New York on Friday and later in other U.S. cities.