"The mother was perplexed as to why we were at that residence," said Greg Fellows, Riverside County Sheriff's Department Perris Station commander.
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According to Fellows, there had been no prior law enforcement contact at the Turpin home.
TIPS: Do you know the signs of child abuse and neglect and what to do if you see them?
The 17-year-old girl called 911 from a deactivated cellphone after she escaped through a window, Fellows said. The teen showed deputies photos of the conditions in the home that led them to respond to the residence to conduct a welfare check and interview David and Louise Turpin.
At that time, deputies found three of the 12 children still in the residence chained to furniture. David and Louise Turpin were subsequently arrested.
"We do need to acknowledge the courage of that young girl who escaped from that location to get them the help that they so needed," said Fellows.
Fellows said the Turpins have lived in Perris since 2014. All of the children, ranging in age from 2 to 29, were home-schooled. They are all the biological children of David and Louise Turpin, Fellows confirmed.
Fellows also said that the family had at one point lived in Murrietta as well as Texas.
Fellows said there was no indication there were other children being schooled at the home.
David Turpin had registered Sandcastle Day School at the home's address. ABC7 reached out to the California Department of Education about why the agency had not conducted an investigation. Under state law, the department does not oversee or inspect private schools.
RELATED: 13 victims, ages 2 to 29, kept shackled in foul Perris home by parents, officials say
The grandparents of the children told ABC News that David and Louise were deeply religious and believed God had called on them to have so many kids.
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Fellows, however, said he had no information on any religious organization that may have played a role in the parents' motives for the abuse of the children.
According to Fellows, the condition of the chained-up and malnourished children, as well as the filthy home, were a shock to investigators. "There was a very foul smell inside the residence. It was extremely dirty," said Fellows.
"I would call that torture," said Fellows.
Fellows said investigators did not yet know how long the children had been kept in those conditions.
Investigators didn't have any immediate information to suggest sexual abuse and there was no indication of mental illness in the family, but many questions still remain, Fellows said.
"We're going to get answers," said Fellows.
The 13 children, some of whom are adults, were removed from the home and transported to local hospitals for evaluation and treatment.
RELATED: Grandparents say 'God called' on Perris couple to have so many children
Grandparents say 'God called' on Perris couple to have so many children
The adult children are listed in stable condition and are being fed in a safe, secure environment, said Corona Regional Medical Center CEO Mark Uffer. "They're very friendly, they're very cooperative," Uffer said.
Uffer said he'd never seen a case like this in his time as the hospital's chief executive.
"And when you see it, almost universally among the staff, people are reduced to tears," Uffer told ABC News. "It's that profound when you see what they're going through. How does this happen?"
Meanwhile, the minor children were being treated at another medical facility.
The Medical Director of the Child Abuse and Neglect Unit at Riverside University Health System, Dr. Sophia Grant, said the children will require stabilization and slow feeding due to their extreme malnourishment.
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"The long-term needs of these kids are going to be psychological and emotional," said Grant. Grant said the children would likely experience post-traumatic stress from their experiences. The recovery of the children will be "ongoing and long-term," she said.
"I think there's always hope, but you have to imagine that these kids are going to need a lot of support," said Grant.
"I would never see him," a woman who lives near the Turpin home, who declined to be publicly identified, said of David Turpin. "But now that it's all coming together, it makes sense. He didn't want no one to come to his door."
She described an uncomfortable encounter her family had last Halloween, when everyone on the block -- except for the Turpins -- decorated their home. According to the neighbor, Turpin made it clear that he did not want any trick-or-treaters approaching his door.
"He said they don't celebrate Halloween, that they weren't giving out candy," the woman said. "But he was outside, sitting in front of a bonfire, holding a cross."
A woman who lives in the home directly behind the Turpin's residence said she never heard the sound of children emanating from the property.
"You never see them, you never hear them playing," said neighbor Kimberly Milligan. "You never see them out in the front. You never saw them."
A 2015 photo shows the 13 identically dressed children flanking their parents after one of the couple's three wedding-vow renewals at the Elvis Chapel in Las Vegas.
Kent Ripley, an Elvis Presley impersonator officiated at several of the Turpins' vow renewal ceremonies, was among those who found the allegations against the parents incredible.
"I didn't get the impression that just because they were thin, that was unusual," Ripley said of the Turpin children. "They were home-schooled, what I found out through the years. So I figured, eh, they're just active.
"They seemed to care about each other. They cared about the kids," he added. "They seemed to smile, the kids were smiling. They didn't hide behind themselves. They were quiet."
David and Louise Turpin remain behind bars with bail set at $9 million each. They are expected to be arraigned Thursday on charges of torture and child endangerment.