The Cuyahoga County prosecutor said he would pursue aggravated murder, attempted murder and assault charges for each day Amanda Berry, Gina DeJesus and Michelle Knight were held captive.
Castro allegedly kept the three confined to his Seymour Avenue home for a decade.
Castro, 52, was arraigned on kidnapping and rape charges Thursday and held on $8 million bond.
"This child kidnapper operated a torture chamber and private prison in the heart of our city," McGinty told an afternoon news conference.
WEWS-TV, Cleveland, quoted a source close to the case as saying that, under police questioning, Castro described himself as a sex addict. The station said he is being kept isolated from other prisoners at the county jail and has been put on suicide prevention.
Berry, 27, DeJesus, 24, Knight, 32, and Berry's 6-year-old daughter were freed Monday after Berry managed to get neighbors' attention. Berry and DeJesus were reunited with their families Wednesday while Knight remained hospitalized. Community members dropped off balloons and other tokens at Knight's grandmother's home in a show of support. A balloon release was planned for Thursday evening.
Castro's brothers, Pedro, 54, and Onil, 50, were arrested along with him Monday but weren't charged in the case. They made court appearances Thursday on unrelated misdemeanor charges.
During conversations with police after her rescue Monday, Knight said when alleged captor Ariel Castro discovered she was pregnant, he would "make her abort the baby," an initial incident report obtained by CNN said.
Knight "stated that he starved her for at least two weeks, then he repeatedly punched her in the stomach until she miscarried," the initial police report said.
When Berry went into labor, Castro ordered Knight to deliver the child, threatening to kill her if the baby died, a police source close to the investigation told CNN.
The baby was delivered in a container to trap afterbirth and amniotic fluid, the source said. Panic followed when the infant stopped breathing.
The women were held in a 1,400-square-foot home, going outside "briefly" twice, Cleveland public safety director Martin Flask said.
The women often would be in different rooms although they interacted and relied "on each other for survival," a law enforcement source with direct knowledge of the investigation told CNN.
Castro would test the women by pretending to leave then returning quickly, the law enforcement source said. If he found indications the women moved, they would be disciplined.
Knight and DeJesus "succumbed" to "their reality," the law enforcement source said.
But "something must have clicked" for Berry Monday, and she escaped, Cleveland Deputy Police Chief Ed Tomba said. With help from neighbors Charles Ramsey and Angel Cordero, Berry freed herself, her daughter and the two other women.
The three women are back with family.
Charging documents indicate Knight was 21 on Aug. 22, 2002, when Castro lured her into his vehicle, then took her to his home.
April 21, 2003, the day before her 17th birthday, Berry accepted a ride from Castro as she was returning home from work.
In April 2004, DeJesus joined them.
Cleveland Police Chief Michael McGrath said on NBC's "Today" show the women were bound and officers found "chains and ropes in the home."
Soon after the three women were found, Castro and two brothers who were with him were taken into custody.
CNN said authorities "found no facts to link" Onil Castro and Pedro Castro to the kidnappings, but they will appear in Cleveland Municipal Court Thursday for outstanding warrants on unrelated, misdemeanor cases.
Several neighbors said they contacted police through the years about activity on Castro's property, such hearing screams and seeing naked women in his yard. Authorities say they received no such calls.
Police said they went to Castro's house twice, once about a fight on his street and once about an accusation of leaving a child alone on a bus, CNN reported.
Court documents from 2005 indicate Castro's former common-law wife accused him of physical abuse, CNN said.
Tomba told CNN he thinks authorities acted properly.
"I'm just very, very confident law enforcement officers ... checked every single lead, and if there was one bit of evidence, [they would have] followed it up very, very aggressively," he said. "In hindsight, we may find out that maybe we did, but that's going to be in hindsight."