LOS ANGELES, United States (AP) — When a 17-year-old girl jumped out a window from the house where her parents allegedly starved and tortured their 13 children, she broke a silence that had likely lasted years.

It’s not clear why the teenager waited so long to act, but psychiatrists say such behaviour is not uncommon even in cases of extreme deprivation.

Most people would recognise milder forms of the same inaction that is a coping mechanism, whether it’s failing to speak out against off-color jokes, enduring sexual harassment or staying in an awful marriage, said Dr Bruce Perry.

“This happens all the time. The number of individuals who would immediately respond to an opportunity where they could get away is very small compared to the number of people who would have that paralysis and insecurity and confusion about what to do,” said Perry, a psychiatrist who is a senior fellow at the ChildTrauma Academy in Houston.

The vulnerable girl might have been shamed, beaten or threatened with violence and only after many missed opportunities did she probably work up the courage to act, Perry said.

“It’s pretty remarkable that she’d do that,” he said. “The power that must have been exerted to keep an entire family like that for so long must have been pretty sophisticated.”

David Turpin, 56, and his wife, Louise Turpin, 49, were arrested Sunday after authorities found the malnourished children in their home in suburban Perris, 60 miles southeast of Los Angeles. They were jailed on US$9 million bail each and are expected to appear Thursday in Riverside County Superior Court on charges that could include torture and child endangerment, authorities said.

Investigators at the home Wednesday removed dozens of boxes, what appeared to be two safes and pieces of a bed frame.

Some siblings were shackled to furniture in the foul-smelling four-bedroom home that looked perfectly normal from the outside.

The couples’ children — ages 2 to 29 — were so emaciated the older ones still looked like children. Authorities thought the 17-year-old daughter who called 911 was only 10 when they found her.

Until the girl fled with photographic evidence, it appears no one, neither neighbors nor public officials, knew anything about what was happening inside.

The Turpins have lived in two Riverside County communities since moving to California in 2011, and police said they were never called to either home, nor were any reports fielded by child protective services.

In Hill County, Texas, where they lived previously, the sheriff’s office received a call from a neighbor complaining that a pig belonging to the Turpins escaped from a pen and ate 55 pounds of his dog food.

In another report, David Turpin said that the family’s dog had bitten their 4-year-old daughter on the face. He told police he took the girl to a hospital for stitches and the dog to a veterinarian to be put down, according to records obtained by The Associated Press.

It’s not clear what motivated the Turpins to live a secluded life with their large brood or what went on in the house. Parents convicted in similar cases exerted control over their children though intimidation, psychological and physical coercion, and frequently possessed their own belief system.

“They develop a kind of cultish doomsday type of religion where the father becomes this mythical leader and the mother and children’s duty is to serve the father,” attorney Ambrosio Rodriguez said.

Rodriguez was a longtime Riverside County prosecutor who sent Jessica Banks, a pastor and mother, to prison for life for beating, starving and drugging her five adopted daughters, who were kept locked in her garage.

The Turpin children appeared to be cut off from the outside world, despite taking trips to Disneyland and Las Vegas, where the parents renewed wedding vows in a service presided over by an Elvis impersonator.

“They weren’t allowed to watch TV. They weren’t allowed to have friends over — the normal things that kids do,” the children’s aunt, Teresa Robinette, told NBC’s “Today” show.

Individuals held under such conditions often become so physically and emotionally weak “that they are unable to free themselves, even if an opportunity arises,” said Dr Allen Keller, who runs the Bellevue-NYU Center for Survivors of Torture in New York. “The abuser has basically taken complete control of them. It is a state of severe helplessness.”

Many victims of abuse suffer from severe depression, anxiety, nightmares and are easily startled in public.

The children were educated in the home. No state agency regulates or oversees private schools in California, but they are subject to an annual inspection by the state or local fire marshal.

The city could find no records of fire inspections, Perris Assistant City Clerk Judy Haughney said in response to a public records request by AP. City Fire Marshal Dave Martinez did not return repeated phone messages seeking comment.

Home schooling can further isolate children, denying them social interactions with peers who aren’t their siblings and also giving the parents the ability to teach whatever they want.

Perry, who led a team of therapists that interviewed most of the surviving children from the Branch Davidian cult in Waco, Texas, said that one 5-year-old could recite whole books of the Bible but could not identify circles and squares.

Other groups have succeeded in keeping their behavior secret by enlisting older children in the rearing and indoctrinating of the younger ones. If older siblings participated in the abuse, they would be less likely to call police.

“I’ve seen this movie before,” Rodriguez said. “It’s going to get more creepy and make our skin crawl. And at the end of it, we’re all going to be asking the same question: ‘How did this happen in front of us and no one noticed?'”