WASHINGTON (AFP) - A life behind bars is just punishment for Ariel Castro, who has pleaded guilty to kidnapping three women and holding them as sex slaves for a decade, his son said on Monday.

"I think it's the best possible sentence," Anthony Castro told NBC television's Today programme, three days after his 53-year-old-father entered a guilty plea in an Ohio court and accepted a life sentence.

"I think if he can't control his impulses, and he really doesn't have any value for human life ... then behind bars is the way he belongs for the rest of his life," he said.

Castro was arrested on May 6 after 27-year-old missing woman Amanda Berry managed to escape from his home in Cleveland along with a young child she bore in captivity.

Police arrived at the scene and rescued Michelle Knight, 32, and Gina DeJesus, 23, from the house. All three had been kidnapped separately, held at the house, chained up and repeatedly raped.

By agreeing on Friday to a prison term of more than 1,000 years on top of the life sentence, Castro dodged the risk of the death penalty.

His son remembered him as "incredibly strict" and temperamental: "He wasn't, you know, a monster 24/7, but if you crossed him, there would be consequences. Those, more often than not, would be physical consequences."

He also said he has no plans to visit his father in prison, stating: "I have no trust in him. I can't see myself going to visit him and giving him the opportunity to face me and lie to me again."