A 14-year-old girl whose body was found buried in her family's yard was kept naked in a dog a cage in their kitchen while alive, a court in the US has heard.

Mary Crocker was bound with zip-ties and locked in the tiny space for so long that her body became hunched and contorted.

She was forced to do all housework and regularly starved, while family members led by her own father and stepmother took turns beating the youngster, the court in Georgia was told on Tuesday.

When she died, she was thrown in a shallow grave dug in the garden – where horrified authorities also found the remains of her older brother, Elwyn Crocker Jr.

The pair’s father, Elwyn Crocker Sr, stepmother Candice Crocker, and three other adult members of the family have all been charged with murder and cruelty to children in a case that has raised questions about domestic child cruelty in America.

The initial charges – and details about them – relate only to Mary, who died in agony last October, the Atlanta Journal-Constitution newspaper reports.

But authorities say they believe her brother – who was two years older – was also abused and charges could arise from his death once medics finish examining the body. He is believed to have died in 2016.

Abby Brown, investigator, told the preliminary hearing at Effingham County Superior Court that Mary would be locked in the dog pen, at the family’s home near the city of Savannah, for more than 24 hours at a time.

She was beaten with household objects including frying pans, Tasered and had her rare meals spiked with pungent substances such as rice vinegar. She was cleaned only when her father - who once worked as a Walmart Santa - dragged her cage into the bathroom to be hosed with water.

At one point, the teenager's joints became so damaged from the confinement that she was duct-taped to a ladder to see if the contortions could be straightened out, Ms Brown said.

A nude photo of her in the cage – taken shortly before her death – was found on her father's mobile, along with text messages exchanged with his wife boasting about the abuse.

Among other evidence set to be given during the case will be testimony from the Crocker’s 11-year-old son James, who told authorities he had been forced to hit Mary with household objects. He himself as cerebral palsy and is now in care.

Authorities have said that, because the children were home-schooled, there was no opportunity to learn of the abuse.

Their deaths only came to light after another relative heard of Mary’s death, and reported it to police, leading to the search of the family yard.

Crocker Sr, 55, Candice Crocker, 33, her brother Tony Wright, 31, her mother, Kim Wright, 50, and Wright’s boyfriend, Roy Anthony Prater, 55, are all expected to deny murder. All have been remanded in custody.

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