Police in the city of Philadelphia, Pennsylvania have arrested four people in connection with the imprisonment of four mentally disabled adults who were kept confined to a basement.

Police arrested one person Wednesday and made three arrests Saturday, charging the suspects with kidnapping, false imprisonment, and other offenses. Bail for the suspected ringleader, 51-year-old Linda Weston, was set at $2.5 million.

Officials say the landlord of an apartment building found the four captives Saturday, locked inside the building's boiler room. Police also found dozens of identification cards and power-of-attorney forms when they arrested Weston. They are investigating whether the suspects were stealing government assistance checks from the captives and possibly other victims.

Weston had served prison time for a crime in the early 1980s, after she was convicted of locking her sister's boyfriend in a closet, where he starved to death.