Sheriff Wesley Kendrick said investigators believe the fire was accidental. Four people made it out of the home — the parents and their two other children.
The body of Molly Holt was found by firefighters in her bedroom under debris where the roof had collapsed, said Chief Deputy Jerry Dorney. Investigators also found a chain and padlock that they determined had secured the girl to her bed, Dorney said.
"The crime scene was very poignant," Kendrick told CBS affiliate KTHV. "To see that child, you could tell that the child was under the bed, trying to get away from the flames."
A metal link chain was looped around the frame and twice around her left ankle, where two padlocks secured her, the deputy coroner told the Arkansas Democrat-Gazette.
"It's my understanding that the child was mentally challenged," Prosecutor David Gibbons said. "In addition may have had some behavioral problems and that's how they dealt with, which is not the right way."
Molly's parents, Lloyd Holt, 32, and Teresa Dick, 31, were arrested on a felony manslaughter charge. At a hearing Wednesday, a judge appointed a public defender to the case and set the bond amount for each of the parents, said Deputy Prosecutor Bruce Wilson.
"Every time I think I've seen everything, you see something new. It just blows your mind," Deputy Coroner Ashley Davis said. "You can't even imagine it."
Investigators believe the fire started in the front of the house, where the girl's bedroom was located.
"The entire house was completely destroyed and on the ground," Dorney said. "The only thing standing was a brick chimney. At this point, we believe the fire was accidental."
The chief deputy would not disclose what the parents told investigators when asked why their daughter was chained to the bed. He said when deputies arrived at the scene, the father said he wasn't able to get Molly out of the house.
Dorney said deputies received a call at 12:45 a.m. Monday of the fire about 13 miles north of Clarksville. The nearest residence to the two bedroom, wood-frame rent house was about a quarter-mile away.
When deputies arrived, the front of the house was engulfed in flames, and Lloyd Holt told them he believed Molly was still inside.
Both parents are employed, although Dorney said he didn't know exactly where. "We've not had any problems with them that I can remember off the top of my head," he said.
The girl had not attended school for at least three years. The state Department of Human Services, citing privacy laws, would not disclose what services, if any, Molly had received.
The couple's other children — a girl about 5 and a boy about 3 — were placed with relatives, Dorney said.