IT is a case of shocking depravity which came to rest in the hills surrounding a picturesque farming community nestled in a valley southwest of Sydney.

Unknown to the 2000 citizens of the town in a fertile valley amid the south-western slopes of NSW, a dark family secret was unravelling.

Now it can be revealed, not only could the case of the Colt family be the nation's most appalling saga of child abuse, it is among one of the worst accounts of incest ever made public.

The NSW Children's Court has taken the rare step of publishing its judgment of actions taken to remove children from the Colt family (a court-appointed pseudonym to protect identification of minors).

Four generations of intimate relations among the Colts had taken place in South Australia, Victoria, Western Australia and finally come to NSW.

Moving state to state, possibly to evade detection, the scandal only came to light when authorities were alerted there were children living in the hills who didn't attend school.

When they turned up on a remote bush block, they uncovered scenes which wouldn't soon be forgotten.

It was an early winter's day last year when officers from the NSW Police and Community Services turned up on one of the blocks which lie around 30km out of the town between large established farms and the untamed scrub of old bushranger territory.

They found 40 adults and children living in two filthy caravans, two sheds and tents on an unsewered block with no running water.

Dirt caked the surfaces of stoves and cooking facilities, rotten vegetables lay in a refrigerator and a kangaroo was sleeping on one of the children's beds.

Exposed electric wires, bags of rubbish and chainsaws lay about.

There were no toilets, showers or baths.

The children were unwashed and wore dirty clothes.

They were shy and made little eye contact.

Few were capable of intelligible speech; almost all had fungal infections in their feet.

Some had oddly-formed features, which scientific tests would later reveal was a result of "homozygosity" or identical gene patterns of both of the children's parents.

The police and welfare officers were taking in the squalor, the deprivation and the fact some of the children seemed developmentally delayed or cognitively impaired.

What they didn't realise was the children were the result of intimate relations between brothers and sisters, and uncles and nieces and fathers and daughters. Their family threw back to a set of great-great grandparents who were a brother and sister.

The family compulsion was regenerating itself.

The children were sexually involved with each other and only one, the youngest, a five-year-old girl, had parents who weren't related.

It was a social time bomb exploding before their eyes.

As one police officer later reportedly told her colleagues, she would never get over it.

Over coming days and weeks, the enormity of what they had uncovered dawned on them.

The five family groups comprised of sisters, Rhonda, 47, Martha, 33, and Betty Colt, 46, who slept every night with her brother, Charlie, and two of Betty's daughters who each had children who proved to be from unions of related parents.

Not only were the children dirty and unschooled, they had multiple health problems and no concept of hygiene.

Betty's son Bobby Colt, 15, had a walking impairment, severe psoriasis and needed urgent dental work.

His speech was not understandable. He wet and soiled the bed and his learning ability was at kindergarten level.

Martha's sons Albert, 15, and Jed, 14, were similarly challenged with their speech, personal hygiene and lack of dentistry.

Betty's 14-year-old son Billy was underweight and not growing properly, had hearing and sight problems, spoke unintelligibly, had an intellectual disability and could barely read or count.

Kimberly Colt, 14, Betty's grandaughter Raylene, was underweight and unable to clean her teeth, use toilet paper or comb her hair.

She had urgent dental problems, hearing, speech and sight issues and was unable to read or write.

She threatened to cut off a caseworker's fingers.

Betty's son Brian, 12, did not understand showering.

He had extensively decayed teeth, and borderline normal hearing.

His eyes were misaligned and he could not read, write, or recognise numbers.

Martha's nine-year-old daughter Ruth was neglected and malnourished.

She was unable to bathe or dry herself. She did not know how to use a toilet or what toilet paper was.

Her features were dysmorphic. She could not read or write, couldn't hear well and her speech was fragmented and stunted.

The caseworkers left and returned again two days later, making a further two visits and finally removed 12 children on July 18, 2012.

Back in town, the locals were unaware of what was unfolding.

As one of the townspeople told news.com.au, on occasional visits two women with "about ten children" would pile out of a car with interstate plates, buy something in the shops and then leave.

"They were never clean looking," the man said, "we always used to make jokes that if you came from that area you'd be inbred.

"But we didn't really know anything about them except those blocks, they might look like a good deal, [40 hectares] for about $20,000 but there's nothing out there, no electricity, no water, just scrub."

Taken into care, the children underwent sessions with psychologists.

The tales they told were harrowing.

Kimberly, 13, reported sexual contact with her uncle, Dwayne, who was nine years old while her aunt, Carmen, 8, watched on.

Sisters Ruth, 7, and Nadia, 9, had sexual touching with their brothers Albert, 15, Jed, 14, and Karl, 12.

On one occasion, three brothers aged 14 years and under tied their sister, 8, and niece, 13, naked to a tree.

The accounts of incestuous underage sex fill pages of court documents.

Clinicians took buccal, or mouth swabs from the children and geneticists deduced five of the Colt children had parents who were "closely related" and another five had parents who were "related".

Interviews with the parents and other members of the family revealed an astonishing tale.

Betty, Martha and Rhonda's maternal grandparents had been brother and sister.

Betty had 13 children, some of whom were probably fathered by her father, Tim, and her brother, Charlie.

Martha's children may also have been fathered by Tim.

Betty's son, Bobby, and Martha's children, Albert, Jed, Ruth and Nadia were the result of closely related parents, as were the three children of Betty's daughter, Tammy, 27, one of whom had died from a rare genetic disease called Zellweger syndrome.

Victorian Police removed Tammy's remaining two daughters when they found her living in a caravan park and she revealed her younger brother, Derek, 25, had fathered all her children.

In the fallout from the discovery of the Colt Family, some children have been placed with foster families, others are in treatment programs for sexualised behaviour and psychological trauma, and they have some contact with their parents and siblings.

They have made progress with schooling and hygiene.

The mothers have taken varying degrees of responsibility for the neglect, the incest or intra-familial sexual abuse which allegedly took place in the family.

Betty Colt, who has supervised contact with her children, appears to be in denial, and her lawyer has disputed the court's findings.

The Children's Court ruled she is not willing "to disentangle herself from her family" and "is incapable of addressing her own traumatic history".

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