A widely publicised Facebook image of David and Louise Turpin with their 13 children is notable for the standard, red T-shirts and blue jeans they are all wearing. At first glance there is nothing especially unusual about the picture other than the large number of children. It fits their neighbours’ comments that this was a seemingly normal family, quiet and undemanding.

At the back, Allen Turpin stands grinning with his mop-head haircut. His wife stands below him, holding their youngest child in her arms, also with a wide smile. It is easy to believe what the lawyers who had had contact with them in earlier years said: there was nothing untoward about them.

The family lived together in a peaceful, well-heeled street about 60 miles south of Los Angeles. The insignificant house had been listed as a private school in 2011, with David Turpin as its principal. He had been an engineer working for the well-established firm Northrup Grumman, but had declared himself bankrupt in the same year he set up the school. His lawyer said this had not been especially traumatic for the family, just a tidying up of their commitments.

Yet one of the girls in this photograph had the wit to run from the house and call the police yesterday. She said that she and her siblings were being held captive against their will.

When the local sheriff investigated, he found some of the children manacled and chained to beds. The conditions they were in were described as filthy, although the details of that horror have not been made public. Neighbours said the children looked emaciated when taken away by the Sheriff, who commented that he was surprised how old some of them were because in their deprived state they looked much younger. A 17-year-old was initially thought to be around 10.

It has emerged that the people held in the house ranged in age from two to 29 years – six children and seven adults kept in appalling conditions. Knowing all this, the Facebook photograph of all of them together posing in red T-shirts takes on a much more sinister appearance.

The children are numbered. It would seem that the numbering is in order of age. The little girl at the front wears a 12, the taller girls behind her are 3 and 5. They all wear the name “Thing” (“Thing 12”, “Thing 3”, “Thing 5”) perhaps in reference to a Dr Seuss book about two characters called Thing 1 and Thing 2. Here is a family that thinks it’s a joke to number everyone rather than give them names and refer to them as “things”.

The photograph of the family together at a chapel in Las Vegas when the couple renewed their marriage vows – something, it seems, they did fairly regularly – shows the considerable trouble they had gone to to dress all the daughters in identical plaid dresses and the sons in identical suits. Here is evidence of the children being treated as decorations for the parents’ rituals. They also show that the Turpins were more than happy to display their anonymous brood, apparently unaware of the social implications of showing them off in such a strangely formulaic way.

Accounts of children being kept captive often relate either to them being part of sexual abuse, as brilliantly portrayed in the 2015 film Room or in the real-life case in Austria where Josef Fritzl kept a woman captive for 24 years and raped her numerous times, resulting in the birth of seven children. There is no suggestion of sexual abuse by the Turpins. And there are, in my experience, a number of different psychological reasons why parents might lock their children away from the world and hold them captive for long periods of time.

One possibility is that the parents wanted to keep their children away from the authorities for religious or other ideological reasons, or because they did not trust those outside the family. These situations have all the qualities of a cult in which the father usually acts as a patriarch who browbeats his wife and children into subservience. The Facebook photographs we’ve seen certainly have the look of a cult about them. Even their picture in Disneyland shows the children identically dressed.

David Turpin would not seem to have limited intelligence, having worked effectively for a major engineering company, nor does it seem likely that he had any obvious mental disturbance if he was able to hold down such a difficult and demanding job. It seems more probable that the couple’s commitment to a large family, without much concern for the resources to look after them, was the starting point for the appalling conditions they have ended up with.

The Turpins are reported to have been married for 27 years, when David was 30 and Louise 22. Not an unusual age difference, but one compatible with him being a dominant man keen to be in control. The eldest person found in the house must have been born at least two years before the couple married, suggesting at the very least a commitment to raising a family from early on. David Turpin’s parents declared to the media today that the couple had a Christian calling to have many children.

Turpin family: 13 siblings who were held captive by their parents Show all 15 1 /15 Turpin family: 13 siblings who were held captive by their parents Turpin family: 13 siblings who were held captive by their parents David and Louise Turpin with their 13 children who were being held captive by their parents in the family home in Perris, California. Facebook Turpin family: 13 siblings who were held captive by their parents Riverside County District Attorney Mike Hestrin speaks during a press conference announcing charges against David Turpin and Louise Turpin in relation to their 13 malnourished children found chained in their home, in Riverside. The two parents were charged with multiple counts of Child abuse, torture, abuse of dependent adults and false imprisonment and could face close to 100 years to life in prison if convicted. EPA Turpin family: 13 siblings who were held captive by their parents The home of David Allen and Louise Anna Turpin, where some of their children were bound with chains and padlocks. Reuters Turpin family: 13 siblings who were held captive by their parents David Allen Turpin poses for a mugshot after being arrested. Riverside County Sheriffs Department via Getty Turpin family: 13 siblings who were held captive by their parents One of the captives, a 17-year-old girl, escaped over the weekend and notified the Riverside Sheriff’s Department. Facebook/David-Louise Turpin Turpin family: 13 siblings who were held captive by their parents Perris residents watch as media gather in front of Turpin family home. The Sheriff's deparmtent said "the parents were unable to immediately provide a logical reason why their children were restrained in that manner." AFP/Getty Turpin family: 13 siblings who were held captive by their parents The children were found in dark and foul-smelling surroundings and "The victims appeared to be malnourished and very dirty,” the department said. Facebook/David-Louise Turpin Turpin family: 13 siblings who were held captive by their parents Neighbours stand outside the home. Getty Turpin family: 13 siblings who were held captive by their parents Louise Anna Turpin poses for a mugshot after being arrested. Not all of their victims were children: of the 13 victims, seven were between the age of 18 and 29, according to the Sheriff's Department. Riverside County Sheriffs Department via Getty Turpin family: 13 siblings who were held captive by their parents David and Louise Turpin in 2015. Authorities arrested them on torture and child endangerment charges, setting bail at $9m (£6.5m) apiece. Facebook/David-Louise Turpin Turpin family: 13 siblings who were held captive by their parents David Turpin and Louise Turpin appear in court for their arraignment in Riverside Reuters Turpin family: 13 siblings who were held captive by their parents David Allen Turpin and his wife, Louise Anna Turpin celebrate a renewal of their wedding vows with Elvis impersonator Kent Ripley in Las Vegas in 2011 A Elvis Chapel via AP Turpin family: 13 siblings who were held captive by their parents David Allen Turpin appears in court for his arraignment in Riverside. Prosecutors filed 12 counts of torture, seven counts of dependent adult abuse, six counts of child abuse and 12 counts of false imprisonment against Turpin and his wife, Louise Anna Turpin. The Press-Enterprise via AP Turpin family: 13 siblings who were held captive by their parents Neighbour Liza Tozier, and her son, Avery Sanchez, 6, drop off his large "Teddy" as a gift for the children. AP Turpin family: 13 siblings who were held captive by their parents Louise Turpin appears in court for her arraignment in Riverside. Authorities say the abuse left the children malnourished, undersized and with cognitive impairments. Reuters

Large families do tend either to be chaotic or to develop formal, often ritualistic, processes to manage day to day activities. Is it possible that, as the Turpins’ finances cycled ever more out of control, they became increasingly coercive in their attempts to handle the situation they had created for themselves?

The world the Turpins created for their family had so little contact with others – Louise didn’t work, David was apparently not sociable and the children were home-schooled – that they may have considered their actions normal. Protecting their children from prying eyes became a way of life. They may have thought that what they were doing was right. But as time went on, they might have become more desperate and only able to control their offspring with threats and chains.

Nevertheless, these children were not totally isolated from the world. At least one of them knew that what was happening to them was wrong. She had that understanding and the temerity to escape and call the police.

A great deal more about the circumstances of the Turpins will doubtless emerge as the case against them is presented to the court. How they managed to create the horrors in their house under the noses of their neighbours without raising any suspicions will become ever more manifest. The revealing world of their Facebook entries will be scrutinised for what the pictures are trying to hide, and will, perhaps, reveal more than anyone could have guessed at the time.