Skylea Carmack had been confined to her room for more than a week, before her stepmother allegedly choked the 10-year-old Gas City girl to death last week, according to court documents.

Grant County prosecutors on Friday formally charged Amanda D. Carmack, 34, with murder, neglect, domestic battery and strangulation in Skylea's death. They’re seeking a life sentence in prison without parole, records show.

Carmack reported Skylea as a runaway at 9:10 p.m. Aug. 31, but by that time, court records say, the girl was already dead.

State Police said they found Skylea's body early Wednesday stuffed into a trash bag and hidden in a shed behind the family's Gas City home.

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According to a probable cause affidavit filed Friday in Grant Circuit Court, Skylea lived in the home with her father Kevin Carmack, Amanda Carmack, three of Amanda's children and three children of Amanda's brother.

Several other children in the home told police that Amanda Carmack was a "strict disciplinarian," who beat them with a pink belt and administered other punishments when they misbehaved, documents showed.

"They stated that when they were in trouble they would have to stand with their face against the wall with their hands in the air," State Police Detective Wendell D. Beachy wrote in the affidavit. "Sometimes they would remain in this position for several hours."

Amanda confined the children to their rooms, police said, only letting them out to eat or use the bathroom. A sibling told police Skylea had been confined to her bedroom for a week-and-a-half before she went missing.

In an Sept. 1 interview with police, Amanda Carmack denied hitting Skylea or the other children with a belt. She admitted slapping Skylea in the face because she caught her stealing a charm bracelet.

Kevin Carmack, a truck driver, told investigators he was driving back from Maryland when he last spoke to his daughter in a video call about 3:29 p.m. Aug. 31. They spoke for about 30 minutes.

A girl sibling told police that Skylea was in her room when the sibling went out to ride a bike between 4 and 5 p.m. but was no longer there when she returned from her ride at about 6 p.m.

Skylea Carmack:Stepmother arrested in 10-year-old's death in Gas City. Missing girl's body was found in trash bag.

On Tuesday, police said Amanda Carmack failed a polygraph test.

At 12:10 a.m. Wednesday, police said Amanda Carmack walked into the Gas City Police Department and confessed.

"(Amanda Carmack) stated she doesn't remember all of the details but she remembers being on top of (Skylea) in the barn," Beachy wrote. "She started choking her with her hands then she thinks she tied something around her neck."

Police found Skylea's body about 3 a.m. Wednesday, curled tight in the bottom of a trash bag. A pair of multicolored pants were knotted around the child's neck.

"(Amanda) wouldn't explain why she had killed her," Beachy wrote, "other than she was very angry."

Contact IndyStar reporter Vic Ryckaert at 317-444-2701 or vic.ryckaert@indystar.com. Follow him on Twitter: @VicRyc.