Police find remains of autistic girl in a pit after she left adoptive parents to live with birth mother

The remains of a missing autistic teenage girl who left her adopted parents and went to live with her biological mother have been discovered in a pit on a Missouri farm.

Savannah Leckie, 16, moved in with her birth mother, Rebecca Ruud, 39, last year.

Ms Ruud has been charged with her murder, abusing a child, tampering with evidence and abandoning a corpse, said Ozark County Prosecutor John Garrabrant.

Savannah was missing before police officers searching for her on Ms Ruud’s remote farm found burned bones and teeth in a fire pit.

Forensic tests later confirmed the remains belonged to Savannah, police said.

Officers also found a meat grinder, knives and 26 bottles of lye, which can accelerate the decomposition of human flesh.

The investigation is still ongoing.

Savannah reportedly returned to living with her biological mother in November 2016 after her adopted parents divorced.

Ms Ruud's ex-boyfriend, Buddy Smart, told investigators he had seen her discipline Savannah by forcing her to crawl through a pig pen and making her to bathe in a pond, a legal document stated.

It added that she admitted this was true and told investigators that when Savannah cut her arm "in a suicidal gesture," she forced the girl to scrub the wound daily with alcohol and salt as punishment.

According to a legal document, Ms Ruud reported a fire on 18 July on her property in Theodosia, a small village near Missouri's southern border with Arkansas.

She told fire officials she was burned trying to save the girl from the fire, but refused to let them talk to Savannah.

Two days later, Ms Ruud reported that Savannah had gone missing, investigators said. She later gave differing accounts of how she was injured but claimed Savannah ran away because she blamed herself for starting the fire.

But Ms Ruud was arrested at a bus station, where she had a ticket to go to Kansas City.

Additional reporting by AP