A retired FBI agent has explained authorities may have taken so long to arrest Lori Vallow for the disappearance of her children because they might be building a bigger case against her that addresses the suspicious deaths of other people in her circle and her apparent fascination with Doomsday culture.

On Friday, after Vallow was arrested in Kauai on an arrest warrant issued by authorities in Idaho, questions surfaced over why it had taken the police so long to take her into custody and what would happen next.

Vallow's two children, JJ, seven, and Tylee, 17, have not been seen since September.

She fled to Hawaii with her new husband, Chad Daybell, after they vanished and has ignored judge's orders and pleas from the kids' extended family to produce them.

As officers prepared to take Vallow away in a patrol her, her Doomsday author husband Chad Daybell (right) watched helplessly

On Thursday, she was finally taken into custody on a charge of disobeying the court order, desertion and nonsupport of dependent children.

Frank Montoya Jr, who retired from the FBI in 2016 after serving since 1991, explained to DailyMail.com on Friday morning that the authorities in Idaho had been forced to hold off until there was any evidence of a crime which, in Vallow's case, there has not been, because both children remain completely unaccounted for.

'What's frustrating is the kids are missing.

Lori in her mugshot on Thursday

'When the parent herself is not cooperating.. it isn't enough to arrest them.

'What's the charge? If it's just child endangerment and she refuses to talk, how do you prove the children have been harmed or more tragically if they're dead? You can't.

'A judge and jury have no choice but to say there's no evidence to hold her in cases like this you'll hugely dependent,' he said.

Montoya went on to explain what will likely happen now to Vallow. He also speculated over the various strands of investigation the police in Idaho now have to look at.

'It's a combination of things that the kids are still missing and the fact she's in Hawaii and they want to talk to her in Idaho. She can either waive or contest - if she contests it then there'll be a hearing, Idaho authorities will present their case. There's little chance that the judge won't extradite.

'[But] there's a number of things they're working through here; the death of her husband, Daybell's former wife, for instance. They're exhuming her body to perform an autopsy.

'He has not been arrested, interestingly. Will he accompany her to Idaho or stay in Hawaii or move on?'

He added that she likely will not be quizzed over the whereabouts of Lori and JJ until she is back in Idaho and that even then, police may want to hold her in a cell for as long as possible to try to break any resolve she may have.

'They'll attempt to talk to her - of course she can invoke her right to silence.

Lori failed to comply with a court order to produce her children before authorities on January 30 in Madison County. Joshua 'JJ' Vallow, seven, and Tylee Ryan, 17, were last seen in Idaho in September in Rexburg, Idaho and authorities are still searching for them

'They have leverage - even though there's a lot of craziness, suspicious behavior and strange stuff, this is not a hardened criminal. She's never spent a few nights in jail.

'What's the prospect of going to jail for 10-14 years. It remains to be seen whether she will cooperate.

Retired FBI agent Frank Montoya Jr

'After spending time in a jail in Kauai, they want to maybe bring her to Idaho and let her sit in an Idaho jail.

'My guess is that they'll wait until they gather back to Idaho,' he said.

He added it will likely not emerge what has happened until her arrest warrant is unsealed.

'This is just another step - this is just another step,' he said.

Another theory he says police may have been worried about is that Vallow and Daybell were obsessed with the Doomsday culture and resurrection.

'The backup in all this is her peculiar ways... there's a bit of a time crunch.

'People like this - what exactly is their intent? Part of these end of the world scenarios is that everyone gets resurrected. Are her kids the test case of that? Until she starts talking who knows... maybe this is the step to get her to start talking,' he said.

The kids vanished in September but the mysterious web of death and Doomsday theories go back months earlier.

Lori's estranged husband Charles Vallow (pictured together) was shot dead by her brother Alex Cox in Arizona on July 11, 2019

Chad's wife Tammy Daybell (pictured together) was found dead under mysterious circumstances in October, just two weeks before he married Lori

In July, Lori's brother, Alex Cox, shot her then estranged husband, Charles Vallow, dead in her home in Arizona.

Lori's brother Alex Cox died under mysterious circumstances on December 12

At the time, they story they gave police was that he was acting in self-defense and that Charles had become angry and out of control.

Alex was not charged. Tylee was there at the time.

In September, Lori moved to Rexburg, Idaho. Late September was when JJ and Tylee were last seen alive.

In mid October, Chad's wife of more than 20 years, Tammy, died mysteriously.

He and Lori got married on a beach in Hawaii two weeks later.

In late November, police in Idaho performed a wellness check on JJ after his concerned relatives contacted them.

Lori said JJ was out of state, being cared for by other relatives.

By the time police realized that was untrue and went back to the house, she had fled.

Then, in December, Lori's brother Alex died in mysterious circumstances.

Throughout January and February, police increased their efforts to find the kids but Lori refused to cooperate.

Rexburg police officers said they were 'astonished' by her refusal to cooperate.