Oscar-nominated documentarian Amy Berg is not the type to shy away from dark subject matter. Her films have probed priestly pedophilia, child murder, casting-couch molestation in Hollywood, and, now, the monumentally icky case of Warren Jeffs, the Utah religious-sect leader convicted in 2011 of sexually abusing under-age female members of his flock. “I’m getting such a bad reputation,” Berg says with a rueful laugh, before pointing out that she also has a big Janis Joplin documentary in the pipeline.

But, first: Prophet’s Prey, which premieres on Showtime tomorrow. The film presents a devastating indictment of Jeffs, but it also raises disturbing questions about his congregation, the Fundamentalist Church of Jesus Christ of Latter-Day Saints, which continues to allow polygamy more than a century after the larger Mormon church abandoned the practice. “These people know nothing else,” Berg says. “They think everyone else is an enemy and they will never make it to the next life unless they follow the law of whoever their leader is.”

Despite repeated entreaties, Berg wasn’t able to get Jeffs to cooperate, but she ended up with plenty to work with anyway: interviews with victims and other former F.L.D.S. members, archival materials including photographs and audio recordings, and the cooperation of two men who have been chasing Jeffs for a decade—the author Jon Krakauer, whose book about the Mormon church, Under the Banner of Heaven, is being adapted into a feature film, and an intrepid private investigator named Sam Brower. “They are just like brothers,” Berg says.

The association with Brower, in particular, immediately placed Berg’s crew under suspicion during their visits to F.L.D.S. compounds. “Every time we went there, we were immediately being followed by the ‘God Squad,’” she says. “That’s what they’re called. I didn’t really worry too much, because we had Sam with us and because we had cameras. But sometimes they would throw things at us. The kids were instructed by their parents, whenever they saw a camera, to just go inside or throw things.”

Stitched throughout the film is the voice of Jeffs himself, delivering sermons in his creepy, low-energy lisp. “After I had heard one sermon, I couldn’t understand how he had so many followers. As a leader of a cult, you just usually don’t see people that are that monotone,” Berg says. “So I wanted to use the sermons to kind of explain to the audience how people are brainwashed, because, unlike other cults, these people are born into it.”

Jeffs himself was the son of the F.L.D.S.’s previous leader Rulon Jeffs, who is said to have left behind 19 or 20 wives and as many as 60 children. After Rulon died, Warren reportedly married all but two of his father’s wives. It’s believed that Warren has as many as 70 wives.

Warren Jeff’s wives pictured beside his portrait. Courtesy of SHOWTIME.

The film explores many of the shocking accusations against Warren Jeffs, including sodomizing a nephew, arranging marriages between men and under-age girls, and marrying girls as young as 12. Berg shows some deeply disturbing photos of Jeffs with his “child brides” and also plays a chilling audio recording of Jeffs having sex with a 12-year-old in a room full of people. “There wasn’t a lot of other material that we withheld,” Berg says. “I like to take the position that, if a jury sees it, the audience will see it.”

Berg’s commitment to exposing such truths—truths most of us would frankly prefer to ignore—is rooted in her understanding that a high percentage of predators have been sexually abused themselves. “There is a connection with all the [criminal activity] that we are fighting against every day,” Berg says, “and I think it’s something that has to stop. It really messes people up.”