The man who kidnapped American teen Jayme Closs at gunpoint after shooting her parents dead in cold blood in a case that shocked the world will be sentenced today.

The brave 13-year-old escaped in January after surviving 88 days as a hostage in Jake Patterson's remote cabin, news.com.au reports.

The 21-year-old had never met Jayme or her parents James and Denise Closs before he stormed their rural property in the tiny town of Barron, Wisconsin in October last year.

He had simply seen Jayme getting on a school bus near her home and decided "that's the girl he was going to take", he told authorities later.

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The sentencing is scheduled to begin at 1.30pm local time before Barron County Circuit Judge James Babler.

Members of Jayme's family are expected to deliver victim-impact statements, and Patterson himself may address the court.

Patterson pleaded guilty at the earliest possible opportunity and refused his right to trial by jury or judge, sparing the teen the horror of reliving her ordeal in the witness stand.

He explained his decision in a bizarre letter sent to a Minneapolis TV station in which he stated he did not want the Closs family "to worry about a trial".

Patterson faces two consecutive life terms for the murders and an additional 40 years for Jayme's abduction. Wisconsin does not have the death penalty.

VANISHED INTO THIN AIR

Police found the bullet-riddled bodies of Denise and James Closs inside their isolated house in the woods near the tiny town of Barron after receiving a cryptic 911 just before 1am on October 15.

When officers arrived at the property just four minutes later, they found 56-year-old Mr Closs dead at the front door, the body of his wife, 46, in the bathroom and Jayme missing.

At the time, authorities struggled to understand how the perpetrator had carried out the murders and gotten away with Jayme so quickly, saying it was as if the teen had vanished into thin air.

For the next three months, hundreds of volunteers — a large proportion of Barron's 3400 residents among them — combed corn fields and woodland searching for Jayme as giant billboards on highways and trucks carried posters of her face.

But there were no clues to her whereabouts or who had taken her and authorities quickly hit a dead end.

Speculation was rife that the teen had run away with a secret boyfriend — perhaps one she'd met online — but investigators shut those down, saying there was no evidence she had gone willingly with her parents' killer.

On January 10, against all odds, Jayme suddenly reappeared in Gordon. She flagged down a woman — who just happened to be a child protection officer — walking her dog and pleaded for help.

The woman took Jayme to a nearby home and called police. Patterson was arrested in his vehicle a short time later. He told authorities he had been out searching for Jayme when he was pulled over.

JAYME WATCHED HER MOTHER DIE

According to a criminal complaint, Patterson had never met the family but told authorities he decided Jayme "was the girl he was going to take" after he saw her getting on a school bus near her home.

He told investigators he plotted carefully, including wearing all-black clothing, putting stolen number plates on his car and taking care to leave no fingerprints on his shotgun.

Jayme told police that the night of the abduction, the family dog's barking woke her, and she went to wake up her parents as a car came up the driveway just before 1am.

While her father went to the front door, Jayme and her mother hid in the bathroom, clutching each other in the bathtub, with the shower curtain pulled shut.

Patterson shot Jayme's father as he stormed the house, then found Jayme and her mother hiding in the bathroom.

He told detectives he wrapped tape around Jayme's mouth and head, taped her hands behind her back and taped her ankles together.

When her mother tried to call 911 he had screamed at her to hang up before shooting her in the head in front of her daughter.

Patterson then loaded Jayme in the trunk of his car and left, narrowly avoiding three police cars, and drove 97km north to his home in Gordon.

'I'M JAYME CLOSS'

For the next three months, Patterson forced Jayme to hide under his bed, barricaded by storage bins containing barbell weights, whenever he had friends over or needed to leave the residence.

He warned her that if she moved, "bad things could happen to her". He also turned up the radio so visitors couldn't hear her, according to documents tendered to court.

On January 10, he told Jayme he was going out for a few hours and she made a snap decision to escape, forcing her way out from under the bed and grabbing a pair of Patterson's shoes.

She fled the house and, struggling in the ill-fitting shoes, ran to a nearby road and cried out for help to Jeanne Nutter, who was walking her dog.

"I'm Jayme Closs," Ms Nutter, a child protection worker, recalled the girl saying. "I don't know where I am," she continued. "Please help, I want to go home."

As sheriff's deputies took Jayme to safety, they set out to look for Patterson. A short time later, deputies saw the car that Jayme had described to them, and pulled him over.

Patterson had been out looking for Jayme and told the officers he knew why they had stopped him, investigators said.

"I did it," he said.

Patterson grew up in the cabin where he held Jayme, according to AP. He wrote in his high school yearbook of plans to join the Marines after graduation, but he was kicked out barely a month after joining up.

He struggled to hold down a job after that, working just a single day at a turkey plant in Barron in 2016 before quitting.

Jayme's parents worked at the same turkey plant, but there's nothing to indicate they knew Patterson. In the criminal complaint, Patterson told investigators he spotted Jayme while heading to work at a cheese factory where he quit after two days.

The day Jayme escaped, Patterson had applied online for a job at a liquor store with a resume that misrepresented his experience.

Laura Tancre, of nearby Star Prairie, said she was relieved by Patterson's plea and "happy for the little girl"

Ms Tancre, 57, worked at turkey plant with Jayme's parents and called them "very nice people."

"I think he should get life for killing both parents," she said. "I'd hate for him to get out and be able to do it again."