We’ve all heard how bad the drug-cartel situation is in Mexico, but Cartel Land director Matthew Heineman actually spent nine months down there with cameras, getting the kind of access that makes you amazed he’s still alive. The documentary, in theaters now, opens on a meth lab in a Mexican forest in the dead of night, and it only gets crazier from there. Heineman embedded not with the cartels but with a citizen vigilante group called the Autodefensas, who are taking their automated weapons from rural town to rural town in the state of Michoacán to flush out the scourge of violence that’s been reigning over the region for years. (He also followed a smaller group of American anti-cartel vigilantes in Arizona.)

Heineman is careful to stress that he’s not a war reporter; his last documentary was about health care, and he’d never been in a combat zone before. Yet through the process of making the film he found himself at the center of shoot-outs, inside places of torture, and surrounded by so much corruption that the line between the good guys and the bad guys became impossible to discern. Kathryn Bigelow was impressed enough to sign on as an executive producer to promote the film, and Sundance gave the movie this year’s U.S. documentary prizes for directing and cinematography. We asked Heineman, who often acted as sole cameraman as well as director and producer, to take us through the craziest things about this insane shoot, which sounds like pretty much everything.

1. All it took to embed with the Mexican vigilante group was an email.

Heineman had spent five months filming Tim “Nailer” Foley, the American vet leading the vigilantes in Arizona, when his father sent him an article about the Autodefensas and their charismatic leader, Jose “El Doctor” Mireles. Heineman tracked down the author, who introduced him to Mireles over email; they were on the phone that night, and two weeks later Heineman was in Mexico. Gaining Nailer’s trust had taken months, but Mireles, says Heineman, “was like, ‘Hey, come on down!’ and I pretty much had full access almost right away.” He also discovered he’d been making the wrong film. “I really thought I was going down there for one or two weeks,” says Heineman, “and I ended up being down there for almost nine weeks, one or two weeks every month.”

2. Shoot-outs are less scary if you don’t know the language.

You’d think that fluent Spanish would be a requirement for making a documentary about Mexican drug cartels. Not so! “I spoke really good bathroom and food Spanish and can understand 50 to 60 percent of the things,” says Heineman, who could “hang and get by” on days when he was shooting by himself but needed live translation for all interviews and any major negotiations.

Multiple times during filming, Heineman found himself in shoot-outs, either initiated by the Autodefensas or perpetrated on them. He and the crew wore bulletproof vests almost every day, but for the first shoot-out that’s shown in the film, of course Heineman wasn’t wearing his. It had been, he says, “sort of a dud of a day,” shooting at a car dealership with an Autodefensa commander who was looking to buy a new ride. “Then, suddenly,” he says, “they get this call like, ‘We know where these two assassins are.’ I was alone, I didn’t have my vest on, and then five minutes later we’re sitting there outside this warehouse that’s having this gunfight with the cartel. And it was absolutely frightening and almost like an out-of-body experience for me.” He kept as calm as he could by focusing on the craft of filmmaking, “focusing on focusing, focusing on exposing, focusing on just making sure that the record button was on,” he says.

Also, not being great at Spanish turned out to be a hidden blessing. “I think if I understood exactly what was being said, I probably would’ve been a lot more nervous,” he says. “I guess ignorance was somewhat bliss at that point.”

3. A Starbucks run might lead to a spontaneous backseat interrogation at gunpoint.

Just riding in the back of a car with Mireles required cojones, says Heineman, “because the guy had a bull’s-eye on the back of his head.” He continued,”You constantly feel the threat of danger around you at all times, and especially as the film went on and the story became much more complicated, it was really scary because you didn’t know if, when you were on an operativo, or a mission, if you were with the good guys or the bad guys.”

Midway through filming, tensions got worse. The Knights Templar cartel had assassinated two or three Autodefensas just driving down the street, and the vigilantes were combing the town to find the assassins. Heineman was at the Autodefensas command center when, again, all of a sudden, the guys started loading their guns and putting on their bulletproof vests. “I said, ‘Where are you going?’” he says. “And they said, ‘Oh, we’re going to get Starbucks.’ And I said, ‘Uh, I think I’m going to go get some coffee with you guys, too.’ So I jumped in the car with them.”

Ten minutes later, bullets started flying toward their car. Heineman kept shooting, for what is the most intense, vérité scene in the film. After a lot of shouting that Heineman didn’t understand, the Autodefensas determined that the shooters were driving a white Jetta and commenced a witch hunt through town. Heineman was in the car with them when they pulled over a man driving not a Jetta but a white SUV, tore him away from his family, bagged his head, and dragged him into the backseat to interrogate him and take him to a makeshift interrogation center. (Where we see dozens of other men like this guy blindfolded and being prodded with guns, Tasers, and handheld shock devices.) “And that was really frightening, being in the backseat as some guy’s pushing a pistol against the guy’s head and trying to get information out of him,” says Heineman. “As a human being, obviously, it’s incredibly uncomfortable to witness, to be next to, to be literally a foot away from. But my job is not to police or to alter what is happening. My job is to document — besides the fact that it would be insane and dangerous if I tried to intervene.”

4. He found the meth lab by just asking around, then almost fucked up the shoot by not having camera lights.

Heineman knew from the minute he stepped into Mexico that he wanted to film a meth lab. “Meth was the lifeblood of the cartel, it was their cash cow,” he says. “Most of the meth that we consume in the U.S. comes from Mexico, and a lot of that from Michoacán, so it was a really important part of the story.” Every shoot, he’d ask people, “‘Do you know somebody? Do you know somebody?’” he says. The leads never panned out, so he gave up.

Then, on their very last shoot, during a terrible day when their car had broken down high in the Sierras in a dangerous area, he says, “We got this call saying, ‘Be in this town square, six p.m. tonight, and you’re in.’” The person who’d called was someone they’d spent months forging a relationship with, and they’d already agreed on ground rules should this ever happen. “Our rule was, ‘I don’t want to be blindfolded or bagged or thrown into the back of a trunk,’” says Heineman. “And in exchange for that, they didn’t want their faces to be shot. I thought that was a pretty fair exchange.”

So they got to the town square, says Heineman, “met a group of armed, masked men, and they drove us through these different towns and pueblos into a field and then basically stopped and said, ‘We’re here to provide protection,’ and then another car drove up and drove us into a lab.”

Heineman had dreamed (literally) of shooting a meth lab for months, and he’d never seen Breaking Bad, so, he says, “I’d always for some reason envisioned this scene in this, like, halogen-lit trailer or something, and we get out there and it’s this ramshackle assortment of things laid out through a forest and it’s almost pitch black.” Problem is, Heineman doesn’t shoot with lights. “So I was like, ‘I waited nine months to get in here and I have no way to film because I can’t see anything!’ And I was, like, freaking out, and the head chef, who’s the guy I ended up interviewing, starts showing me around the process of cooking with this little flashlight, and it’s with that flashlight that we filmed the scene.” (The chef also told them that they’d learned their cooking process from an American father and son.)

5. The problem with shooting a meth lab is that everyone gets high on meth.

The process of cooking meth takes several days, so the head chef invited Heineman and his crew to come back the next night. They established a meeting spot, but the next night the cooks blew them off. Same thing the next night, same thing the third night. Finally, it was their very last day of shooting in Mexico, so Heineman talked to his fixer and made the executive decision to drive into the forest to find them. He figured the guys knew who they were and trusted them, and it was during the daytime, so it would be okay.

What we don’t see in the film is the hours the crew spent terrified, waiting by a highway as car after car drove up to ask them why they were there. Finally, a car escorted them not to the forest but to a pool hall where all the chefs, not just the ones Heineman knew, were gathered. “It was crushing me not to film there,” he says. “But I knew that if I brought up the camera then not only was it potentially dangerous, but it might hurt our ability to get back into a lab.” He did, however, discover a big reveal that ends the film.

It took more hours still to get the green light to go back to the forest. But when they got there, the chefs didn’t recognize them. “They had been cooking for three or four days,” says Heineman, “so all the chefs were super-high and paranoid. And it took a long time to calm them down. They thought we were DA, they thought we were all sorts of things, and we’re like, ‘No, no, we’re the same guys who were here the other night. It’s all good.’” Heineman and Co. eventually managed to get the chefs to cooperate, but also inadvertently discovered firsthand what had been going on in their heads. “We didn’t get high per se,” says Heineman, “but definitely being near and inhaling some of those fumes was somewhat mind-altering, not in a good way.”

6. However questionable the vigilantes’ actions, the cartels were doing worse.

The film shows photos of lynched bodies and decapitated heads, but Heineman never saw them in person. He did, however, interview members of a town where the cartel had ritually executed 15 people working in a lime field, 13 of them from the same family, including women and children, as retaliation for their employer’s failure to pay a tithe. As Mireles says, “We are all survivors; they’ve attacked our families, raped, captured, and killed someone we loved.”

Heineman felt that his job was to find the humanity in that chaos and to bring home the idea that this is happening in our backyard. “We talk about ISIS, we talk about all these horrible groups around the world,” he says, “but there’s a war that’s happening in the country just south of us, a country that we share so much history with, a country that we share a border with. 80,000 killed since 2007, 20,000-plus people disappeared since 2007.” He wanted to tell the story of the resilience of “people living in a lawless world, living in a world without sort of any government institutions, and if there are government institutions, they’re colluding with the cartel. They have to fight back because they have no one to turn to.”

The scariest part of filming, says Heineman, was not “these bang bang moments, per se,” but an interview he did with a woman who described being kidnapped by the cartel with her husband and watching him being chopped up to pieces in front of her and then burned to death. “To be in the room with this woman and see her body that was there, to look into her eyes that were still deeply hollow — it was almost as if her soul was sucked out of her,” says Heineman. “And to hear her describe the horrors of what they did with her husband and to think about how we’re the same species. People don’t do that to other people. That stayed with me much more so than anything else.” (And even after that, he says that the thing that frightens him most of all is the Mexican government.)

He was so shell-shocked that the first time he went back to Mexico was last week for the opening of the film down there, which he says was incredibly emotional.