A woman who allegedly chained four mentally disabled adults in a Philadelphia basement had identification documents for as many as 50 people, it has emerged.

Police allege Linda Ann Weston, 51, stole disability benefits, and say the documents suggest her fraud extended far beyond the four known victims.

Weston previously served a prison sentence for starving a man to death.

Gregory Thomas, 47, and Eddie Wright, 49 were also charged.

Philadelphia police said Weston had dozens of ID cards, power-of-attorney forms and other documents, the Associated Press reported.

The FBI has joined the investigation, and police are looking into additional federal charges.

"We have to determine exactly what happened," FBI Special Agent JJ Klaver told the AFP news agency.

"You've got a horrific crime here. You've got vulnerable people who were severely mistreated."

Police found the four victims on Saturday, locked in a sub-basement room with a dirt floor. They were undernourished and had bed sores.

The adults found in the basement have the mental capacity of 10-year-olds, police said, and were imprisoned in a room they could not stand up in, with only a container of orange juice.

Three of the victims were emaciated and had sustained injuries which they said were the result of beatings.

'Real dirty'

They ranged in age from 29 to 41. All four have been treated at hospitals and were placed with social service agencies.

Turgut Gozleveli, the owner of the Philadelphia building, told the Philadelphia Inquirer he checked out the basement after neighbours complained of suspicious people.

When he failed to find anyone in the basement, he followed the sound of a barking dog to a room under the basement, where a chain was wrapped around a door handle.

Inside he saw two small dogs and blankets, and then people's faces.

"It was terrible," he said. "Something I never expected to see in my life."

One victim said he met Weston through an online dating service.

"That was real dirty of [her]. That was wrong," one of the four victims, Derwin McLemire, told a local TV station on Monday.

He and two others said they had been on the move for about a year with their alleged captors, travelling from Texas to Florida to Philadelphia.

"I escaped one time to one of the houses that we used to live in, of hers, and I didn't get away so they got me."

Starvation death

Linda Ann Weston and Eddie Wright recently lived for about two months at a home in West Palm Beach, stripping it of wire and plumbing and smearing faeces on the walls, according to a report by the Palm Beach Post.

The FBI is investigating whether there may have been more victims in other US states.

Almost 30 years ago, Weston was convicted of starving to death 25-year-old Bernardo Ramos, after Ramos had refused to support her pregnant sister.

She was sentenced in 1985 and spent eight years in prison, according to reports.