(CNN) -- Wisconsin authorities have jailed the father, stepmother and stepbrother of a 15-year-old girl investigators say was kept in a basement, sexually abused and starved before being found last week.
The teenager weighed only 70 pounds when a passerby found her barefoot and in her pajamas February 6, according to a Madison police report. A doctor who examined her described her as a victim of "serial child torture with prolonged exposure to definite starvation," the report states.
The girl's 18-year-old stepbrother has been charged with three felony sexual abuse counts, according to court records. Her 40-year-old father and 42-year-old stepmother have been charged with child abuse and recklessly endangering a child, both felonies, as well as a misdemeanor count of child neglect.
CNN's policy is to withhold the names of victims of allegations of sexual abuse and those of their family members.
Investigators learned the girl was kept in the basement of her home with little food and no bathroom, the police report states. When she was found, her weight was more than 30 pounds below what the U.S. Centers for Disease Control and Prevention lists as the median for her age.
The girl's 40-year-old father and 42-year-old stepmother were arrested on child neglect charges, police said. Neither the girl nor her relatives were immediately identified.
When the girl was taken to a hospital, her father "provided medical explanations for her physical condition," the report states. But a hospital social worker raised doubts about his account, and investigators learned the girl had been the subject of a prior abuse claim in 2007.
The girl did not back up the third-party allegation at that time, and the family did not cooperate with investigators, according to the report.
CNN's Deanna Proeller contributed to this report.