"Some even believe him to be God on Earth," explains Utah Attorney General Mark Shurtleff.
Not that you'd guess that by looking at him - 52-year-old Warren Jeffs comes across as rather ordinary. But as leader of the radical FLDS, he is anything but. His critics believe he has transformed the church from a quirky religion to something much more sinister today.
"There's a certain brand of FLDS under Warren Jeffs that is also, I believe, similar to an organized crime group," says Shurtleff, who says he sees parallels to the mob in the FLDS' organization, finances and lack of respect for the law.
The best example of that, Shurtleff says, is the practice of underage marriage. "I've gone on record as calling them the American Taliban, in the way they treat women," Shurtleff tells correspondent Susan Spencer.
Utah Private investigator Sam Brower has been keeping an eye on the FLDS for years, first helping members who'd left the group, and later working with law enforcement.
"He controlled every detail of a person's life. Where they work, who they're gonna marry, where they're gonna live, almost down to when they're gonna have sex and why," says Brower, who has a pretty low opinion of Jeffs.
Wherever they are, members accept on total faith whatever the prophet tells them. "He came in one day and decided that dogs were evil," Shurtleff explains. "And every single dog in town was eliminated."
"They've been totally brainwashed and brought into this culture that's taught them they're gonna go to hell if they deviate from it," Brower says.
Before Warren Jeffs, his father Rulon was the group's prophet. When he died six years ago at age 92, Warren, who by then was helping run things anyway, formally took power and became the new prophet. He sealed the deal by marrying many of his father's wives.
"Warren has somewhere between 50 and 80 wives," Brower tells Spencer.
Jeffs has resisted all attempts to stop underage marriages. And 48 Hours has obtained a copy of a birth certificate which may help explain why: it names Jeffs the father of the baby; the mother was underage when she got pregnant.
Brower says young girls are routinely married to older men. "I know that the FLDS wanna make this about religion. They wanna make it about polygamy. But that's not it. It's about child abuse. It's on a scale that's never been seen before in this country," he charges.