Neighbors and friends were stunned by the arrest of Castro and his two brothers after a 911 call led police to his house, where authorities say three women missing for about a decade were held captive.
Castro and his brothers, ages 50 to 54, were in custody Tuesday but have not been formally charged.
Ariel Castro was friends with the father of Gina DeJesus, one of the missing women, and helped search for her after she disappeared, said Khalid Samad, a friend of the family. He also performed music at a fundraiser held in her honor, Samad said.
"When we went out to look for Gina, he helped pass out fliers," said Samad, a community activist who was at the hospital with DeJesus and her family on Monday night. "You know, he was friends with the family."
Tito DeJesus, one of Gina's uncles, said he played in a few bands with Castro over the last 20 years. He remembered visiting Castro's house after his niece disappeared, but he never noticed anything out of ordinary, saying it was very sparse in furniture and filled with musical instruments.
"That's pretty much what it looked like," DeJesus said. "I had no clue, no clue whatsoever that this happened."
Juan Perez, who lives two doors down from the house, has known Castro for decades.
"He was always happy, nice, respectful," Perez said. "He gained trust with the kids and with the parents. You can only do that if you're nice."
He said Castro had an ATV and a motorcycle and would take children on rides. Nothing seemed wrong with it then, he said, adding that he now thinks that was one way Castro tried to get close to the children. He also worked until recently as a school bus driver.
Castro's personnel file with the Cleveland public school district, obtained by The Associated Press through a Freedom of Information request, shows he was hired in 1990 as a bus driver after saying on his application that he liked working with children.
The personnel file includes details on his dismissal, approved by the school board last fall after he left his bus unattended for four hours.
Police identified the other two suspects as the 52-year-old's brothers, Pedro Castro, 54, and Onil Castro, 50.
Lucy Roman lives next to a house that she said is shared by Pedro Castro and his mother. She said police arrested him Monday night.
"I feel sorry for her," Roman said of the mother. "She's a very nice lady."
Several residents said they saw Ariel Castro at a candlelight vigil for the missing girls.
Antony Quiros said he was at the vigil about a year ago and saw Castro comforting Gina DeJesus' mother.
One neighbor, Francisco Cruz, said he was with Castro the day investigators dug up a yard looking for the girls.
Castro told Cruz, "They're not going to find anyone there," Cruz recalled.
Castro's Facebook page identifies him as a Cleveland resident and graduate of the city's Lincoln-West High School. His interests include Virginia Beach, the Chinese crested dog breed and Cuban-born salsa singer Rey Ruiz.
On April 11, he wrote to congratulate "my Rosie Arlene" and wish her a fast recovery from giving birth to "a wonderful baby boy. That makes me Gramps for the fifth time. Luv you guys!"