SEOUL, South Korea — Kim Dong-chul, an American businessman in Rason, a North Korean special economic zone near the border with Russia, was leaving a local government office on Oct. 2, 2015, when he was stopped by a 34-year-old army veteran he had hired as a secret informant.
“Chairman Kim, here is the information you wanted,” the man said, tossing a yellow envelope into Mr. Kim’s car, before rushing away. In the envelope were a computer memory stick, documents and photographs of a ship docked at a nearby port. Mr. Kim hadn’t gone several yards before his car was stopped again by an officer from the Ministry of State Security, the North’s infamous secret police.
Mr. Kim knew he had just been set up, but it was too late.
It was the beginning of a 31-month incarceration in North Korea that included torture, a conviction on espionage charges and forced labor in a prison camp. Mr. Kim was the longest-held American in North Korea when Secretary of State Mike Pompeo flew there in May last year. Mr. Pompeo returned home with Mr. Kim and two other American hostages, a triumphant moment for President Trump.
Now, in a memoir entitled “Border Rider,” published in South Korea in June, Mr. Kim, 65, recounts how he became a decorated foreign investor in North Korea, then spied for the Central Intelligence Agency and South Korea’s National Intelligence Service, and ended up as Prisoner No. 429.
“I try not to blame anyone for what happened to me. I am just lucky to come out of North Korea alive,” Mr. Kim said in an interview in the South Korean capital, Seoul. “But I am sorry for those six North Koreans who worked for me as spies and were executed.”
Mr. Kim was born in Seoul in 1953. In 1980, his father, a civilian worker for the United States military in Seoul, urged him to emigrate to the United States, where Mr. Kim eventually became a Baptist pastor and also ran a cleaning business.
In 2000, with his wife, an ethnic Korean from China, Mr. Kim moved to northeast China as a missionary. The following year, Mr. Kim applied for entry into North Korea, using his wife, who had relatives in the North Korean power elite, as a bridge. In 2002, Mr. Kim became a resident in Rason, where North Korea was eager to attract foreign investors. Mr. Kim poured his entire savings, $2.8 million, into building and operating the five-story, foreigners-only Tumangang Hotel.
He quickly learned that to be successful, he had to win the trust of the party and military elites of the brutal totalitarian regime with regular cash donations.
He forked over $400,000, a third of his hotel’s annual revenues, to the North Korean government, and partnered with military-run trading companies to help build their fisheries exports. He donated buildings for schools and hospitals. He received three government awards after supplying German-made massage machines, jade beds and other gifts for Kim Jong-il, the late father and predecessor of Kim Jong-un, the current leader of North Korea.
“I had to do business with them to establish myself among them and realize my true and original goal of missionary work,” said Mr. Kim. “But I had a conflict with myself. I was walking the line between the two worlds.”
As Mr. Kim built his connections as a rare resident American in North Korea, United States and South Korean intelligence agents began approaching him when he traveled to China and South Korea, Mr. Kim said.
The agents provided him with spying equipment, like a camera hidden in a wrist watch and an eavesdropping device, as well as operational funds, he said. In return, they wanted information on the North’s nuclear and missile programs. Mr. Kim paid his informants and leveraged his access to the military elites to find and meet retired nuclear scientists and former and active-duty military officers who served in weapons facilities.
“The more I learned about North Korea, the more I was confused and curious, wondering how on earth this kind of regime could ever survive,” Mr. Kim said. “I decided to do whatever it took to learn as much as I could, and eventually to share my knowledge with the intelligence officials, never thinking that it might come to this end.”
The spying claims Mr. Kim made in his book could not be independently confirmed. Neither the C.I.A. nor the South Korean intelligence agency responded to requests for comments.
While he was held in North Korea, Mr. Kim, as other hostages often did, appeared in a government-arranged news conference and apologized for his anti-state crimes. But unlike other hostages who denied the statements after their release, saying they were coerced, Mr. Kim said the North Koreans’ findings on him were essentially true, although he also said they had tortured him to uncover his spying activities.
Mr. Kim was interrogated for nearly seven months, first in Rason and then in a safe house in Pyongyang. His handlers made him kneel at a bathtub, with his hands tied behind his back, and pushed his head into the water. Mr. Kim said he passed out twice.
Mr. Kim was sentenced to 10 years in prison and sent, blindfolded, to a labor camp outside Pyongyang on April 29, 2016. There, as Prisoner 429, he was forced to toil from 8 a.m. to 6 p.m., six days a week. In winter, guards made him dig holes in the frozen ground and then fill them. The prison menu never changed: brown rice, fermented-bean soup and three pieces of pickled turnip. Mr. Kim supplemented his diet with berries, roots and even grubs, a source of much-needed protein.
“Many times, I wanted to kill myself,” he said. “But it was a place where you could not kill yourself even if you wanted to. How could you, when eight armed guards watched you 24 hours a day, taking turns?”
The prison, a ramshackle nine-cell facility, had only two inmates: Mr. Kim and Lim Hyeon-soo, a Korean-Canadian missionary sentenced to hard labor for life in late 2015. Only once, when they ran into each other under tall corn stalks while the guards were not watching, could Mr. Kim and Mr. Lim talk to each other, whispering their names.
Then in August 2017, Mr. Kim was ordered to clean Mr. Lim’s empty cell. A guard told him that Mr. Lim, Prisoner No. 36, had been released.
“I was happy for him, but I felt as if I had lost an arm or leg,” Mr. Kim said.
Unbeknown to him, help was on the way, too, for him, as United States officials negotiated to free him as part of their efforts to arrange the first summit meeting between Mr. Trump and Kim Jong-un in Singapore in June last year.
But Mr. Kim had no idea what was happening when guards came to him the morning of May 9 last year and told him to change into his old civilian clothes. He was taken to Pyongyang, where he was ordered to write a statement of apology and escorted to a United States government plane.
When he and two other Korean-American hostages, Kim Hak-song and Kim Sang-duk, went onboard, a cheer broke out inside the plane. And when the plane landed at Joint Base Andrews outside Washington early next morning, another surprise awaited: Mr. Trump came on board to welcome the hostages home. Until his release, Mr. Kim did not know Mr. Trump was the president of the United States.
Mr. Kim and his wife have since resettled in New York, where one of their two daughters lives.
Mr. Kim lost all his investment in North Korea when he was expelled. The torture left him with two crooked fingers, chronic back pain and a limp. The intelligence officials he once worked for have not contacted him since his release. His wife told him to “forget” and move on.
Mr. Kim planned to publish the English and Japanese editions of his book to help the world better understand the country he said he “both loved and hated.”
“It’s neither socialist nor communist,” he said when asked about North Korea. “It’s a country with the tightest dictatorial and slave system you can imagine.”