An alleged sexual assault on an Upper Darby girl led police to a house full of young, Liberian women - some of them pregnant - who may be involved in international human trafficking.

Now, police are anxious to locate the women, who disappeared after authorities started asking questions and arrested a woman who was posing as their mother.

The investigation began when a Beverly Hills Middle School student on juvenile probation told her probation officer that her mother had forced her to watch pornographic films while she probed the girl's private area with her fingers, Upper Darby Police Superintendent Michael Chitwood said.

The girl, who told police she was 13, said that another adult woman was present in the room during the assault.

When police began investigating, the girl changed her story and said that the assailant was not her mother, but rather someone who brought her and several other girls from Liberia and posed as their mother, Chitwood said.

"Which indicates to us, this could be a prostitution thing, a human-trafficking thing," he said. "In the end, she's not the mother of any of these kids."

The woman, Ophelia Cheayee, 34, of North Church Lane near Harrison Avenue, was arrested Dec. 11 on charges of aggravated indecent assault, possessing obscene and indecent materials, and corruption of a minor.

"She admits she did it," Chitwood said. "There was no 'I did it because.' It was just a 'I didn't think it as a big deal' kind of thing."

Police said up to eight people were living in Cheayee's rowhouse, at least five of whom were girls who told police they were 13 to 17 years old.

But police can't be sure of their names or ages, or even the name and age of the alleged victim because none of the girls had identification, Chitwood said.

"Who she is, what her real name is and what her real age is is something we don't know at this time," he said.

Chitwood called in U.S. Immigration and Customs Enforcement, who have the "capacity to do more worldwide checking than we do," he said.

U.S. Customs did not return calls from the Daily News.

According to police, it's not clear whether the girls - or even Cheayee - are in the country legally or how they got here.

"There's a whole lot of questions that have to be answered in respect to their immigration status," Chitwood said. "There are many unanswered questions and certainly, the defendant holds the key to a lot of them."

The answers may be even harder to come by now, since as of Monday, many of the girls had left Cheayee's home.

"The other, younger girls in there have since disappeared," Chitwood said. "When the police started getting involved, they were kind of gone."

The teenagers were left at the home because there was another adult present and police did not have "the appropriate legal right to put them anywhere else," Chitwood said.

Other individuals involved in the "caper" aren't being identified at this time, Chitwood said, including a man from another community who may be charged with raping the middle-school student who said she was molested.

The girl told police that her father lives in Malaysia and her mother lives in Morocco, Chitwood said. She was placed in a Delaware County juvenile detention center for an alleged assault in an unrelated incident at her school, he said.

"I'm concerned for the status and safety of the young girls," Chitwood said. "When you look at this type of thing, when nobody is aware of it until they go to school and there's a report, you have to think how much is going on undiscovered throughout the Philadelphia area and the rest of the country?"

Cheayee was in the Delaware County Prison on $100,000 bail. *