Nanjing railway police said on Tuesday that a girl photographed as she was being fondled by a man in a crowded railway station waiting room had been adopted by the man's parents.

The 18-year-old man, surnamed Duan, is from Huaxian county, Henan province, and was detained after the pictures were released online, the police said.

They are investigating whether the girl was properly adopted. Under China's Adoption Law, his parents may not be qualified, police said.

The foster parents appeared to ignore their son's fondling of the girl, who is about 10 years old, at the crowded Nanjing South Railway Station for at least five minutes. They also told him to leave when they noticed people around were taking pictures, according to witnesses.

Some pictures went viral on the internet after being uploaded by Chen Lan, a writer and NGO worker on Saturday. The pictures showed that the man put his hands inside the girl's dress and on her breast.

The police have asked netizens not to spread details about family members or the case, in an effort to protect the girl's identity.

"People may easily identify them if too many details are exposed," the police said. "To prevent the girl from being hurt again, don't spread details."

The police are negotiating with the civil affairs department of Huaxian county to move the girl to a safe place.

Lan Tianbin, a lawyer at the Dongheng Criminal Defense Center in Nanjing, said child molesters can be sentenced to up to five years in prison.

"Under the Criminal Law, molesters committing the crime in public places can be sentenced more than five years," Lan said.

Courts in China dealt with 10,782 cases of child sexual abuse from 2013 to 2016, according to the Supreme People's Court.

The Girls Protection Special Fund of the China Foundation of Culture and Arts for Children, found in a survey that most child sexual abuse victims under 14 years old were abused by people close to them, such as a teacher, neighbor or relative.

Sun Xuemei, who works for the fund, said the country must educate children about how to avoid sexual assault.

"Sexual assault prevention is as important as fire prevention and traffic safety education. But it doesn't exist in most Chinese families and schools."

Also, according to a survey by the fund in 2016, nearly 70 percent of Chinese families have never provided sexual assault prevention education to their children, and 90 percent of children never receive any such lessons in school.