Mr. Do faced an agonizing predicament. He wanted to provide as much information as he could to establish that the book was not a hoax. But he also had to protect Bandi’s identity to keep him safe from retaliation by the North Korean regime. This is about all Dr. Do will say about Bandi’s identity: He was born in 1950. He has belonged to the Korean Writers’ Alliance, a government-controlled organ dedicated to producing censored literature for state-run periodicals of the North.

Image “The Accusation: Forbidden Stories From Inside North Korea,” by Bandi. Credit... Patricia Wall/The New York Times

“The Accusation” was published in South Korea in 2014 by Chogabje.com, a conservative news website and publisher, but failed to gain much attention. Mr. Do persisted, pitching the manuscript to publishers abroad. A breakthrough came when a French translation was released last year. Other translations quickly followed.

Mr. Do said that the last time middlemen checked on Bandi, nine months ago, he was safe and was aware of his book’s publication in the outside world. A regular guest on a South Korean radio program broadcast into the North, Mr. Do has been providing updates on the book, hoping that Bandi will hear him. “The Accusation” has earned $10,000 in royalties. Any profit will be used to support Bandi’s family and books by defector writers living in South Korea, Mr. Do said in an interview.

Only a handful of people have been allowed to examine the original manuscript. Mr. Do recently let a reporter for The New York Times check it, but did not allow it to be photographed, fearful that the North Korean regime might be able to identify Bandi by scrutinizing his handwriting.

As an additional protection, Mr. Do said that he altered the names of the characters and locations in the stories. “I assumed that they were fictional in the first place,” he said. “But I did not want to take chances. The more he is known, the more I am worried about his safety.”

Kim Joeng-ae, a former North Korean propagandist now in Seoul, is a member of North Korean Writers in Exile PEN Center, a branch of PEN International, the literary and human rights organization. She said that she and other writer defectors had studied Bandi’s stories and concluded that they were indeed written by a North Korean.

There are expressions in his book that only a North Korean would be able to write, she said. (The version published in South Korea has footnotes to guide readers though words only used in the North.) His stories also closely followed the “seed theory,” a guideline of all North Korean writers, which requires them to structure their writing tightly around a core ideology — though Bandi uses the same device to attack the party line.