Prosecutors have charged a couple who allegedly imprisoned their 13 children in a Southern California home with torture, child abuse, false imprisonment and a lewd act against a child.

In announcing the charges against David and Louise Turpin, Riverside county District Attorney Mike Hestrin described an alleged escalating ordeal of beatings, imprisonment and starvation that stretched across years and multiple different residences, ending only after the siblings executed an escape plan years in the making. The children were deprived medical care and taunted with food and toys that the parents refused to share with them, he said.

Appearing in court for the first time since their arrest, they both pleaded not guilty on all counts. Their bail was set at $12m (£8.6m), with the next court date set for February.

The charges cover alleged offences stretching back to 2010 and encompassing both the city of Perris, where their children were discovered last weekend during a police raid, and their previous home in Murrieta. Mr Hestrin said the abuse began before that, when the family lived in Texas, a time when the parents lived apart from their children and occasionally visited to drop off food

“The abuse and severe neglect intensified over time and intensified as they moved to California,” Mr Hestrin said as he laid out the allegations at a press conference, adding that it is believed to have progressed from “neglect“ to “severe, pervasive, prolonged child abuse”.

“There are cases that stick with you, that haunt you,” he added. “Sometimes in this business we’re faced with looking at human depravity, and that's what we’re looking at here.”

If convicted on all counts, the two Turpin parents could face 94 years to life in jail.

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

Without providing details on the alleged abuse, Mr Hestrin said the lewd act charge involved Mr Turpin allegedly subjecting a child under the age of 14 to unwanted touching.

Investigators have struggled so far to explain a potential motive for what they discovered after one of the Turpin children – a 17-year-old so malnourished authorities initially believed she was a child – escaped through a window and contacted authorities to say she and her siblings were being held captive. She had planned the escape for more than two years, Mr Hestrin said, and a sibling who initially fled with her turned back in fear.

Mr Hestrin said that siblings were held in captivity starting “many years ago”. They were initially bound with ropes but after one escaped, the parents began using chains and padlocks to trap and punish the children, he said, often keeping them shackled as they relieved themselves. They were barred from showering more than once a year.

“One of the reasons for these punishments of being chained up to a bed,” he added, was when “the children were found to wash their hands above the wrist area. They were accused of playing in the water and they would be chained up”.

The siblings suffered beatings, strangulation and punishments that “would last for weeks or even months at a time,” Mr Hestrin said. When not bound by chains, he said, they were locked in different rooms.

They were allegedly deprived of basic medical care: none had seen a doctor in more than four years, he said, and none had ever been to a dentist. When asked whether there was medication or pills in the residence, Mr Hestrin said, one of the children appeared not to know what those were.

Medical examinations have found signs of severe malnutrition, cognitive impairment and nerve damage Mr Hestrin said. A 12-year-old had the weight of an average 7-year-old; a 29-year-old weighed only 82 pounds. They were deprived of food, with some being taunted by food being set out, but then the children could not consume it.

“They would buy food including pies – apple pies, pumpkin pies – leave it on the counter, let the children look at it but not eat,” Mr Hestrin said.

That alleged taunting fit into what Mr Hestrin described as a broader pattern of apparent psychological torment. The children were not allowed to have toys, but there were “many toys found in the house that were in their original package and had never been opened,” he said.

“This is severe emotional, physical abuse,” he said. “There is no way around that.”

The Turpins homeschooled their children, with California approving Mr Turpin’s request to manage a private school out of his home, and Mr Hestrin said evidence suggests they did not learn much.

“They lack a basic knowledge of life,” Mr Hestrin said. “Maybe the children didn’t know what a police officer was”.

Mr Hestrin said the family's habit of sleeping all day – often going to bed around dawn – and being active at night may have helped explain why the siblings were not discovered for so long.

“People who commit these kinds of crimes have to hide those crimes,“ he said.