“He said it was nothing dishonest,” Dr. Montalbert-Smith said in an interview in San José, “that lawyers had written papers, that they are not paid donors. But if a foreigner comes here and the donor doesn’t know him and says he is an altruistic donor, the chance that it is trafficking is very high. I told him, ‘No thanks.’ It wasn’t easy to refuse.”

Dr. Mora did not respond to repeated requests for an interview, and his lawyer declined to comment.

The Costa Ricans who provided kidneys to foreigners were mainly men who had not finished high school and were either unemployed or held low-income jobs.

Two of the donations were arranged by Dimosthenis Katsigiannis, a Greek immigrant to Costa Rica, according to a search-and-seizure order obtained by The Times. Mr. Katsigiannis, 56, owns the Akropolis pizzeria, which at the time was across from the public hospital where Dr. Mora worked.

According to his lawyer, Mr. Katsigiannis received a call in 2009 from a relative who needed a transplant. He inquired among the doctors who frequented his restaurant and was directed to Dr. Mora. Then he let it be known that he was shopping for a donor.

The 38-year-old man who offered his services for about $5,500 was so satisfied that his older brother sought out a comparable deal, said Mr. Katsigiannis’s lawyer, Jesús Gilberto Corella Quesada. Mr. Corella said that Mr. Katsigiannis received no compensation. The brothers received their payments at the pizzeria, according to the search order.

“Obviously there was some money involved,” Mr. Corella said. “Nobody would donate, except if they were related or a friend, without being paid.” He disputed the brothers’ affidavits vowing that they took no money.

Subsequent sellers were recruited by Maureen Cordero Solano, 33, a police officer who drove a taxi after hours, according to the authorities. Like many who fall into organ brokering, Ms. Cordero had sold her own kidney in 2009 and met Dr. Mora in the process. She received $1,000 from him for each donor she supplied, according to the search order. She could not be reached, and her lawyer would not comment.