"We have no idea who some of these people are," Evers said.
The three people arrested were a 51-year-old Texas man, taken into custody at the scene, and 50-year-old woman and a 48-year-old man arrested Saturday night. The woman had relatives who lived in the building, though those relatives did not appear to know anything about the four prisoners in what Evers described as "a dungeon."
The names of those arrested were not released until they were formerly charged, Evers said. Charges included kidnapping, conspiracy, aggravated assault, and reckless endangerment.
"We're going to find every crime possible in the crime code to put on these individuals," Evers said. That could include federal crimes for kidnapping across state lines, and the FBI is involved, he said.
The discovery was made about 10:40 a.m. in the 4700 block of Longshore Avenue.
Little said Northeast Detectives and the Police Department's Special Victims Unit in the investigation.
The four were taken to Aria Health Frankford, where they were being fed and evaluated, Little said.
They were in stable condition, Little said, though they suffered from malnutrition.
"The conditions they were living in were deplorable," she said. "It was not good."
Evers said the room included buckets for urine and feces.
Early Saturday evening, neighbors in the city's Tacony section gathered across the street from the two-story apartment building, which has a tan stucco facade and six doorbells at the front entrance.
A police officer stood in the doorway, allowing residents to enter and exit, while other officers cordoned off the front of the building.
Neighbors said officials also removed two small dogs that appeared also to be malnourished.
Shirley Kramer, who lives a block from the apartment building, said one of the people taken from the building had been removed on a stretcher and placed in an ambulance.
"I never knew what was going on here. You can't believe stuff like this," Kramer said as children rode bicycles and scooters on the sidewalk across from the apartment building.
Inside the building, residents peeked out first-floor windows at police and TV news teams steps away from the entrance.
Joan Sendef, who lives several blocks away, said she heard that police had come to the building because of a landlord-tenant dispute.
"You think you've seen it all," Sendef said. "When it lands in your front door, it's really heartbreaking. It's so sad; these are human beings."
Contact staff writer Vernon Clark at 215-854-5717 or firstname.lastname@example.org.