The three women had been hospitalized and released following their rescue. Knight was re-admitted to the hospital on Wednesday in good condition, a spokesman said.

Euphoria over the rescue of the women on Monday was giving way to mounting questions about how their imprisonment in a house on a residential street had gone undetected for so long.

Aunt Sandra Ruiz (L), father Felix DeJesus and mother Nancy Ruiz (2nd R) speak to the media just before Gina DeJesus arrives at her home in Cleveland, Ohio, May 8, 2013. [Photo/Agencies]

Several neighbors said they had called police to report suspicious activity at the house in a dilapidated neighborhood on Cleveland's West Side, but police denied those calls had been made.

"We have no record of those calls coming in over the last ten years," Cleveland Police Chief Michael McGrath said on Wednesday on NBC's "Today" show.

McGrath said he was confident police did not miss opportunities to find the missing women. "Absolutely, there's no question about it," he said.

Agents from the Federal Bureau of Investigation were searching through the house where the women were believed to have been held since vanishing, McGrath said.

"We have confirmation that they were bound, and there (were) chains and ropes in the home," he said.

No human remains were found, Cleveland Safety Director Martin Flask said in a statement.

McGrath said the women had been allowed outside "very rarely" during their captivity. "They were released out in the backyard once in a while," he said.

Cleveland Mayor Frank Johnson said on Tuesday that child welfare officials had paid a visit to the house in January 2004 because Castro was reported to have left a child on a school bus while he stopped for lunch at a fast-food restaurant. But no one answered the door and the ensuing inquiry found no criminal intent, officials said.

Questions have mounted about why the women's captivity escaped notice.

"We didn't search hard enough. She was right under our nose the whole time," said Angel Arroyo, a church pastor who had handed out flyers of DeJesus in the neighborhood.

Aside from the school bus incident in 2004, city officials said a database search found no records of calls to the house or reports of anything amiss during the years in question.

"We have no indication that any of the neighbors, bystanders, witnesses or anyone else has ever called regarding any information, regarding activity that occurred at that house on Seymour Avenue," the mayor said.

Israel Lugo, a neighbor, said he called police in November 2011 after his sister saw a girl at the house holding a baby and crying for help. He said police came and banged on the door several times but left when no one answered.

About eight months ago, Lugo said, his sister saw Ariel Castro park his school bus outside and take a large bag of fast food and several drinks inside.

"My sister said something's wrong ... That's when my mom called the police," he said. Lugo said police came and warned Castro not to park the bus in front of his house.

Another neighbor said a little girl could often be seen peering from the attic window of the Castro house.

Born in Puerto Rico, Ariel Castro played bass in Latin music bands in the area. Records show he was divorced more than a decade ago and his ex-wife had since died. He is known to have at least one adult daughter and son.