“One hundred percent, yeah, man, America First, bro,” he said in a telephone interview from the Washington area.

His father, Dr. Fitaihi, 54, had founded a private hospital in Jidda and became a well-known motivational speaker. He was among more than 200 wealthy Saudis arrested in November 2017 in a roundup that was portrayed as a crackdown on corruption. But Mr. Fitaihi said his father had told the family he did not know of any allegations or evidence against him.

“There is no reason whatsoever,” the son said.

Most of the others detained at the same time as Dr. Fitaihi have since been released. But his son said the former detainees and their families are afraid to talk to one another, and his family believes the government has warned them to avoid contact with one another as a condition of their release. “Everybody is in a bubble,” he said.

Mr. Fitaihi said he had been visiting his father’s medical office in Jidda when a group of plainclothes security officers came for the doctor. The son said he received special permission from the Saudi authorities to leave the kingdom last year in order to look after the family’s assets abroad, since their wealth inside the kingdom had been frozen.

Much of the information that the family has learned about Dr. Fitaihi since his arrest — including the account of his torture — came from a few days in January 2018 when he was allowed out of prison to visit a son in a hospital after surgery. Dr. Fitaihi “was half his size and very emotional,” Mr. Fitaihi said.

The family initially hoped that the Saudi authorities would quickly release Dr. Fitaihi on their own, or that quiet appeals behind the scenes would secure his release.