SOURCE
Two of them may have been held captive in various locations around the United States for as long as 11 years, police said.
The victims, who all had the mental capacity of 10-year-olds, were discovered chained to a boiler in a tiny 15ft by 15ft basement room behind a steel door that was chained shut.
Philadelphia police Sergeant Joseph Green said: "This is just a horror story. They were abused physically and emotionally."
Three people have been charged with holding the victims as part of what is believed to have been an extended social security fraud.
Linda Westen, 50, a convicted murderer, allegedly posed as their caregiver while cashing their disability benefit cheques.
She and two alleged accomplices, Eddie Wright, 51, and Gregory Thomas, 48, were charged with kidnapping, aggravated assault and false imprisonment.
Police said two of the captives were held for 11 years and referred to Westen as "Mom."
They travelled with her as she moved from city to city, including stops in Texas and Florida.
The other two had been with Westen since February, and all of them arrived in Philadelphia earlier this month.
Sgt Green said the basement cell had contained "a couple water bottles but no food or anything. There was a bucket they used to urinate in."
The room looked like a Cold War-era bomb shelter and the ceiling was too low for an adult to stand up.
It contained a mattress with some bedding and a flat board with a pillow.
Officers were investigating a report of squatters in an apartment building when they found the victims.
They were taken for "much needed medical attention" at hospitals and were "doing well," police said.
The victims were a 29-year-old woman and three men aged 31, 35, and 41.
Philadelphia police spokesman Ray Evers said interviewing them had proved difficult and officers were trying to establish their identities.
He said: "We have no idea who some of these people are."
