CHICAGO (AFP) - The brothers of the US man charged with kidnapping and raping three women, locking them in his home for a decade, said they hope he "rots" in jail, in an interview aired on Monday.

He's a "monster. Hateful. I hope he rots in that jail," Mr Onil Castro, 50, told CNN.

"I don't even want them to take his life like that," he said, referring to a possible death penalty charge in the case. "I want him to suffer in that jail."

Brother Pedro Castro, 54. said: "I feel the same way,"

The two brothers were arrested soon after Ariel Castro on Monday, when three women held in captivity and a daughter born to Ariel, were discovered at his home in Cleveland, Ohio.

But Pedro and Onil were later released, with police saying there was no evidence they participated in the crimes.

In the interview, both said they had no idea what was happening.

"If I knew that my brother was doing this, I would not be, not - in a minute, I would call the cops because that ain't right," Pedro said.

"If I knew, I would have reported it, brother or no brother," he added.

The brothers said they never went past the kitchen in Ariel's house, where the three women were kept hostage, explaining that Ariel kept the rest of the house blocked off with curtains and played the television or radio to block out sounds.

"Something had to be on at all times in the kitchen. So I could hear nothing else but the radio or the TV," Pedro said.

The two said they were kept separate from Ariel at the jail, but Onil saw him at least once.

Ariel said "Onil you're never going to see me again. I love you, bro," the brother recounted.

Ariel Castro, a 52-year-old unemployed bus driver, was arrested after one of the victims, 27-year-old Amanda Berry, managed to call out to a neighbour, who kicked in the door to the suspect's home and rescued her and her six-year-old daughter.

Police arrived on the scene and entered the house, finding two more women: 23-year-old Gina DeJesus and 32-year-old Michelle Knight. All three had been snatched in separate incidents around a decade earlier.

Onil said he was especially horrified because they knew the father of DeJesus and Ariel even went to vigils for the teen girl and hugged her mother.

"Felix, I know that you are out there listening, and you know that I was concerned about your daughter, and I had not even the slightest idea that this would be going on with," he said, according to an excerpt posted on CNN's website.

But both brothers said the feared they would never fully be freed of the suspicion raised after police announced their arrest and made their mug shots public.

The two, and their 71-year-old mother, are in hiding, saying people have thrown rocks at their homes and sent them death threats over the Internet, CNN reported.

The prosecutor has said investigators would go back over the many torments Castro allegedly inflicted on the women during their long ordeal, with the aim of bringing additional charges, including ones that may carry the death penalty.

Castro was ordered held on a US$8 million (S$9.92 million) bond on Thursday.