In an affidavit that reads like gothic fiction, investigators describe how a teen reunited with her birth mother last year on an isolated farm in Missouri - only to be tortured there, forced to crawl through hog pens and have salt rubbed in her wounds, and then finally murdered last month and burned in a fire pit.

Rebecca Ruud, 39, was arrested Monday by Ozark County sheriff's deputies and charged, among other crimes, with the first-degree murder of Savannah Leckie, whom she had given up for adoption at birth, 16 years before.

The baby had been taken in by a husband and wife in Minnesota, according to sheriff's documents, and raised there nearly all her life.

But Savannah's adoptive parents eventually divorced, and by late 2016 the teen was having trouble getting along with her adoptive mother's new boyfriend.

In November 2016, Ruud, who had been in casual contact with Leckie for years, "agreed to take Savannah back and she was delivered to Ruud in Ozark County," wrote a sheriff's deputy, as he recounted all the things the girl would subsequently endure.

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A truck driver and volunteer firefighter, Ruud lived on an 81-acre farm near Theodosia - close to the Arkansas border, miles from the nearest paved road.

In photos on Ruud's Facebook feed, life after reuniting with her daughter appeared idyllic: all baby goats and pretty dresses.

"She looks just like you," a friend wrote beneath a photo of mother and daughter last December.

In June, Ruud announced that the pair had even started a family business, making soap, according to the Ozark County Times.

"She wanted this so badly," she wrote on Facebook of her daughter. "To combine two landmark events, her Sweet 16, and the official opening of Our Hidden Holler Farm soap business."

But offline, a sheriff's investigator wrote, the girl's new life was bleak.

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"Savannah has been home-schooled and has almost no social contact," he wrote.

She lived, slept and studied on a property with a generator providing the only electricity,and a well pump for water.

Ruud and her boyfriend slept in a converted metal building, like a barn, the deputy wrote in the affidavit. Savannah slept beside them in a camper with a broken air conditioner.

"Savannah's inability to adapt to life on the farm" became a growing irritant to Ruud, according to the affidavit.

Eventually, she worried that the cost of caring for the girl would cost her the farm.

"It's to the point that I either need more help to care for her, or I can do nothing with her," Ruud allegedly wrote to Savannah's adoptive mother in late June, a few weeks before the girl disappeared.

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On July 18, Ruud reported a fire burning at the top of a hill on her property. Less than an acre of brush had burned, and firefighters put it out.

But when they returned to the family's makeshift living quarters and asked for water, Ruud refused, according to the affidavit. She said Savannah got a small burn in the fire, and was laying down and couldn't be disturbed.

Ruud wouldn't let anyone close to the girl's camper, the firefighters reported.

Two days later, Ruud called the sheriff's office. Her daughter had disappeared overnight, she reported. Her favorite pillow, blanket and coloring kit were missing.

"I think she's a runaway," Ruud said, according to the affidavit. "Savannah is blaming herself for the fire."

Rescuers fanned out across the woods and fields. A helicopter and plane searched from above, and missing posters went out as day passed with no sign.

Investigators began to get suspicious.

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Ruud brought Savannah's computer to the local fire department on July 24, according to the affidavit, and asked a technician there to examine it.

"I considered this to be unusual considering law enforcement were actively searching for information leading to Savannah's disappearance," a sheriff's deputy wrote.

The same day, an ex-boyfriend of Ruud's told investigators he'd seen the girl crawling through hog pens and bathing in ponds before she went missing. The man said Savannah had once cut her arm, an investigator wrote, and "Ruud scrubbed the affected area with alcohol and salt on a daily basis as a form of discipline."

Ruud and her current boyfriend, Robert Peat Jr., were interviewed at the sheriff's office, according to the affidavit, where the mother allegedly admitted to rubbing salt in Savannah's cut, wrestling the girl in the mud of a pig pen, and other severe forms of discipline.

But the couple were becoming less and less cooperative as the search went on, an investigator wrote.

Deputies returned to the farm on Aug. 4 - with dogs, state police and a search warrant. They now suspected that Savannah had never left the property.

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The farm looked different that morning, an investigator wrote. Gates and doors that had been open on previous visits were now chained and locked.

Some time after investigators arrived, an affidavit states, Ruud and Peat abruptly left their home.

They drove for nearly 100 miles, to Summersville, Missouri, and married each other there, on the same day police combed the farm.

Investigators searched carefully - around the barn and the camper where Savannah had lived, and the vacant buildings and derelict vehicles that surrounded it.

A few hundred yards from the residences, they found a pile of fresh leaves and branches. The brush pile was speckled with cigarette butts and surrounded by what a deputy described in the affidavit as "charred earth."

The searchers lifted the brush. A deposit of light ash lay beneath it.

In the ash, they sifted out a button, imprinted with little ducks, and finger bones and vertebrae and teeth.

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The bones were human, a forensic investigator in Springfield, Missouri, told the Ozark County sheriff. They'd been burned at a very high temperature, and had deteriorated so badly that she suspected some chemical was used.

The sheriff mentioned the Hidden Holler Farm soap-making enterprise, according to an affidavit, and that his deputies had seen drums of chemicals on the property. He mentioned that soap was made with caustic lye.

"That would do it," the forensic investigator said. So the sheriff got a second search warrant.

Deputies returned to the farm on Aug. 9. The goats and the couple's guns had disappeared, they noted.

They went back over the property, and the ash pile they'd searched before. According to documents published by the Ozark County Times, investigators left with a box of girl's clothing; hair; a knife; a meat grinder; and more than two dozen bottles of lye.

"We're dealing with someone who's tried to dispose of evidence," Ozark County Sheriff Darrin Reed told OzarksFirst.com.

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Reed didn't immediately return a message about the case. Ruud could not be reached, and it's unclear if she has a lawyer.

But as investigators studied evidence seized from the farm and continued to investigate this month, they learned that Ruud and her new husband had purchased bus tickets to leave the state.

So they asked for an arrest warrant this week.

"I believe Ms. Ruud deliberately and methodically caused the death of Savannah Leckie and then attempted to conceal it by destroying evidence and her remains by fire," a sheriff's deputy wrote to a judge, who signed the request and issued the warrant.

Two Greyhound busses were to leave Springfield on Monday, according to the affidavit - taking Ruud to Kansas and Peat to Tennessee.

The sheriff, Reed, and two deputies drove to the station, arrested Ruud and returned her to the Ozark County jail.

She was charged Tuesday with first-degree and second-degree murder, fatal abuse of a child, tampering with evidence and abandoning a corpse - and "more charges are forthcoming on any individual that was involved in aiding or tampering in this investigation," Reed wrote in a news release.

The sheriff told the Ozark County Times he wants the mother put to death.