Zion raid: The ranch has not yet revealed all its secrets...

Despite rescuing hundreds of children from a sect, police are still in the dark. Andrew Gumbel reports

It began with a panicked phone call from a 16-year-old girl, speaking from deep inside one of America's weirdest and most secretive religious compounds. She was, she said, a 16-year-old who had been forced into marriage a year ago with a 49-year-old man – a member of a fundamentalist Mormon sect practising an extreme form of plural marriage – who beat her, held her against her will and had now impregnated her with her second child.

The girl's name has not been made public. In fact, the authorities aren't even sure who she is or where she might now be. A first attempt to arrest her husband appears to have turned up the wrong man. Still, her phone call was the break they had been seeking for four long years to move against the extraordinary fundamentalist Mormon compound that had sprung up out of nowhere in the remote Texas town of Eldorado.

The initial search warrant made possible by the phone call turned into a full-blown operation to take away and protect as many children as the incoming police officers could find. Last week 416 children and teenagers – and 139 adult women – were taken into care after a mercifully peaceful raid on the Yearning for Zion ranch.

The images from the ranch are like something from another century – women and children in plain, loose-fitting clothes and simple shoes or sandals, looking scared and lost and oddly out of step with the times. As, indeed, they are.

The police and child protection services knew as soon as the Eldorado ranch was built in 2004 that the fundamentalists were polygamists, with a track record of marrying off girls as young as 14 or 15 to church elders who might be in their 70s or 80s. They knew the only reason the Fundamentalist Church of Jesus Christ of Latter Day Saints – or FLDS for short – had set up in Texas at all was because the law was bearing down, at last, on their long-standing settlement in the twin cities of Hildale and Colorado City on the Utah-Arizona border.

They even had an informant – almost certainly a former FLDS member – letting them know what was going on behind the walls of Yearning for Zion. Without a direct witness account, however, they did not have probable cause to make a move. Now they had it, and they didn't waste a second.

A detachment of Texas Rangers, along with local officers, swooped on the ranch 10 days ago – just ahead of the 6 April anniversary of the founding of the Mormon religion – and told the acting leader, Merrill Jessop, that they intended to search the place from top to bottom "at whatever cost that may be".

Those were not idle words. Rumours had been flying for years that the FLDS members at Eldorado were armed to the teeth, and that they had installed a high-grade incinerator for the express purpose of destroying human remains. Their "prophet" and leader Warren Jeffs, now serving prison time for his role in arranging the forced marriage of a teenage girl in Utah, has a reputation as a hardliner and a man who inspired great fear even in his own followers.

Nobody in America, meanwhile, could launch a raid on a fringe religious group without remembering the Waco disaster of 1993, when the FBI managed to set fire to a ranch belonging to the Branch Davidian sect at the end of a tense 51-day siege, killing 80 people.

All that Jessop and his followers offered, however, was passive resistance. Perhaps it would have been a different story if Jeffs were still there; perhaps the stories about him were exaggerated. About 60 church members fell to their knees sobbing and formed a ring around the large temple building at the centre of their community. Jessop refused to unlock the heavily bolted temple door, obliging police to call in experts who forced it open with the help of hydraulic tools.

The Mormons also played an elaborate shell-game with their children, moving them from house to house in a futile attempt to prevent at least some of them from being taken away. Their attitude, carefully cultivated by the leadership, was that any outsider to the community was an agent of Satan, so they certainly weren't about to co-operate, or even talk. The authorities ended up spending six days clearing the ranch of all but a few dozen adult males, who are staying put for now.

Of all the physical evidence gathered by investigators – genealogical records, financial accounts, computers, safes and so on – perhaps most eerie was a series of bedrooms on the third floor of the temple where the church's "spiritual" marriages are believed to have been consummated. On one of the beds they recovered a female hair, which they hope will help to bolster their case that the entire church operation is essentially a racket to turn teenage girls into sex slaves.

These are highly incendiary charges, and are not without political risk to the police and prosecutors. In the early 1950s, the then Governor of Arizona, Howard Pyle, ordered a raid on the twin fundamentalist communities on the border with Utah. Instead of earning praise for smashing a dangerous cult, however, Pyle was lambasted for separating mothers from their children and failing to respect the fundamendalists' freedom of religion, and the episode ended his political career.

Things are a little different now, because times have changed and because Texas, unlike Arizona or Utah, has little or no native Mormon population to fan the flames of anti-government outrage. Still, some of the mothers from the Eldorado ranch have wasted no time in crying foul against the authorities.

"My children were kidnapped for no reason. They are being held hostage," a woman calling herself Mrs Johnson told a Utah newspaper. "They won't let them talk to me or let me see them. They need their mother. I am a good mother and I want to be with my children."

There are signs that the systematic refusal of the fundamentalists to co-operate with the authorities is creating considerable confusion. The police may well have a problem if they can't locate that 16-year-old girl, and they have plainly been confused by the huge numbers of people with the same name – multiple Barlows, Jessops and Jeffses. The man they arrested was Dale Barlow, but he claims never to have set foot in Texas. They might have been muddling him with Dan Barlow, who was mayor of Hildale and Colorado City, or with Sam Barlow, a one-time close confidant of Warren Jeffs, or any number of people with the same name.

Long-time observers of the FLDS say the confusion is part of a long-standing strategy of trying to wrongfoot the authorities. In fact, the FLDS has long had an overt policy of trying to sting the government for everything it can – in the form of food stamps, tax breaks and subsidies. An FLDS member will generally declare his first marriage and take the tax benefit, then let his subsequent wives claim welfare as unemployed single mothers. Down the years, the church has earned hundreds of millions of dollars in public funds this way, a process it describes derisively as "bleeding the beast".

The FLDS broke with the mainstream Mormon church as far back as 1890, when the political leadership of Utah renounced polygamy as a condition of attaining statehood. Culturally, however, polygamy remained a concept attracting great sympathy far beyond the FLDS itself for many decades, making it difficult for prosecutors or politicians to intervene.

The extremism of Warren Jeffs has made things considerably easier, however. Although his predecessors were hardly moderates, he pushed things to new limits as he took over from his father six years ago. Jeffs forced his followers to learn his sermons verbatim, banned books, television and music, established a cultural enforcement squad known as the Sons of Helaman to carry out terrifying spot checks, broke up families that incurred his displeasure and "reassigned" wives and children to different men. He himself is believed to have taken more than 70 wives.

So many people were expelled from Hildale and Colorado City that he soon had a mini-rebellion on his hands, and that in turn emboldened the public prosecutors in both Arizona and Utah. With the number of allegations growing, Jeffs secretly bought up 1,700 acres in west Texas and established a new community there.

Although FLDS followers live in simple, almost poor conditions, the community is strikingly well endowed. They set up a limestone mining operation at the Yearning for Zion ranch, along with a waste-water treatment facility and a cement plant. They made sure they were self-sufficient so as to avoid all contact with the outside world.

Local residents became instant experts on the group – books on polygamy soon beat John Grisham for popularity at the local library – and waited for the moment to break open the sinister, secretive world of their new neighbours. That moment has now come, its outcome still uncertain.