(CNN) -- A Wisconsin man who stumbled across and alerted authorities to a young girl investigators say was kept in a basement, starved and sexually abused, said Tuesday she looked much younger than her 15 years -- "like she just came from Auschwitz."
Mike Vega of Madison was on his way home from buying milk at the store when he saw what looked to be a girl, "8 or 9 years old," he said, outside, wearing pajamas but no shoes. Temperatures were below freezing.
"I thought that was odd ... So I put the car in reverse and rolled down the window and asked her if she was OK. She said no, she needed help," Vega told CNN's Brooke Baldwin.
He described picking the girl up, putting her in his car, wrapping her feet in a coat and blasting the heat.
"Her eyes were set back like she was very dehydrated. You could see the bones in her arm ... The only way I could best describe it is she looked like she just came from Auschwitz," said Vega. Auschwitz was a concentration camp in Poland operated by the Nazis during World War II.
They began to talk. Soon into the conversation, he stepped outside the car, telling the girl he needed to call a friend. He dialed 911.
The girl's 18-year-old stepbrother has since been charged with three felony sexual abuse counts. 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.
"Mr. Vega was in the right place, at the right time, and did the right thing," said Madison Police Chief Noble Wray. Efforts are under way to establish a fund for the victim, who is being "well cared for," he added.
The teenager weighed only 70 pounds when Vega found her on February 6, according to a Madison police report, more than 30 pounds below what the U.S. Centers for Disease Control and Prevention lists as the median for her age. A doctor who examined her described her as a victim of "serial child torture with prolonged exposure to definite starvation," the report states.
According to a criminal complaint, investigators learned the girl was kept in the basement of her home with little food and no bathroom.
She ran away because she was afraid and upset with her stepmother, who controlled her movements and told her when she could use the bathroom and eat, the complaint reads.
It states the girl has gained more than 17 pounds this month, even though doctors have restricted her intake because "she is gorging so much that she has been throwing up."
When the girl was taken to a hospital, her father "provided medical explanations for her physical condition," the police report reads. 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.