MADISON, Wis. -

Prosecutors have charged the 18-year-old stepbrother of a severely malnourished Madison girl with repeatedly sexually assaulting her beginning around her 10th birthday.

Dane County prosecutors on Thursday also filed felony child abuse and other charges against the 15-year-old girl's father, Chad Chritton, and stepmother, Melinda Drabek-Chritton.

The girl told police the couple had kept her confined to the basement of their Treichel Street home since 2006 and that they beat her, starved her and forced her to eat feces.

The couple is facing charges of first-degree reckless endangerment, intentional child abuse (bodily harm) and child neglect.

Prosecutors said the girl's stepbrother first sexually assaulted her around December 2006, then again from February 2009 to February 2010.

The 18-year-old stepbrother, Joshua P. Drabek, has been charged with first-degree sexual assault of a child under age 13 without great bodily harm, sexual assault of a child under age 16 and intentional child abuse (bodily harm).

A driver spotted the girl Feb. 6 walking barefoot in pajamas near her home on Madison's southeast side and called police. The driver said the teen was so scrawny he mistook her for an 8-year-old.

According to the criminal complaint, the girl fled the house after she was told by her stepmother that if she didn't hurry up and pick up some papers, Drabek-Chritton would take a knife and slit the girl's throat.

The girl weighed just 70 pounds when she was found, and the doctor who examined her determined she was severely malnourished. A doctor who specializes in child abuse examined the teen on Friday and diagnosed her condition as "serial child torture with prolonged exposure to definite starvation," according to the criminal complaint.

The attorney for Drabek-Chritton on Thursday argued for reduced bail.

"She is currently unemployed. She doesn't have any income of her own at this point," said attorney Adam Welch.

But the court commissioner increased Drabek-Chritton's bail to $30,000, citing the severity of the allegations.

"There also appears to have been ongoing sexual abuse at the hands of Joshua Drabek, who lives in the home, with the knowledge of Mr. Chritton along with his now-wife, Melinda Drabek. It also appears this family in the past has not cooperated with either the Department of Human Services or the Madison Police Department in investigations involving similar conduct by Joshua Drabek," said Assistant District Attorney Matt Moeser.

The bail for Chad Chritton was increased slightly as well, and Joshua Drabek will remain in jail on a probation hold.

Complaint Details Abuse Allegations

The criminal complaint is offering more details about the abuse allegations.

The family forced the teen to spend most of her time in the home's basement, without a bathroom, and she received little food, the complaint said.

The complaint said the girl, identified as SLC, told investigators she was mostly confined to the basement because her family members had "trust issues" with her and believed she posed a threat to them.

Chad Chritton told investigators that he had full custody of SLC because her biological mother had married a sex offender in Texas, the complaint said. SLC told police that when she was living in Texas with her mother and stepfather that her stepfather sexually assaulted her "once in a while when (she) was 8," the complaint said.

The complaint said that Chad Chritton told a doctor and a social worker that SLC was locked in the basement with bars on the windows and an alarm on the door so they would know if she tried to get out of the basement. Chad Chritton also told them he has cameras by the pantry to monitor if SLC ate anything because he believed SLC is diabetic and that sugar caused bad behaviors in SLC, the complaint said. No medical doctor has ever told SLC that she has diabetes, the complaint said.

SLC told investigators that when she does go upstairs, she's allowed to eat oatmeal and peanut butter and jelly sandwiches, "but that she frequently eats out of the trash or off the floor so as not to set off the alarm," according to the complaint.

SLC confirmed there was no bathroom in the basement and said that she sometimes had to defecate or urinate in containers or on the floor, the complaint said. SLC said she did this because she didn't want to set off the alarm, get anyone upset or wake anyone up by doing upstairs to the bathroom, the complaint said.

The girl said her father and stepmother made her drink her urine "a couple times I think," while she had been forced to eat her feces "lots" -- that she thought it was less than 10 times but couldn't say for sure because she didn't kept track, the complaint said.

The girl told investigators she hadn't urinated or defecated in the basement for awhile because she limits what she drinks so she doesn't have to urinate or defecate too much.

"If I drink water, then I will pee and I don't want to pee in the basement. I'm underweight because I don't eat much. I've always wanted to eat more," SLC told investigators, according to the complaint.