But once he made it there after a harrowing border crossing, nothing went as expected.

The woman disappeared. Mr. Kwon ended up with a human trafficker who promised to get him to South Korea, for about $2,500. After an arduous journey that lasted a month, he arrived in the South in November 2014, settling in Ulsan, an industrial city in the southeast.

But like other defectors, he struggled to make the transition from the North’s highly regimented totalitarian system to the South’s fast-paced, hypercompetitive capitalist society. (About 63 percent of defectors say they experience discrimination in the South, according to a study by the government-run Korea Institute for National Unification last year.)

Mr. Kwon drifted from farm to construction work. He was often ridiculed for not understanding the English words South Koreans liberally adopt in their daily conversation. Just over 5 feet tall, Mr. Kwon didn’t see a future in physically demanding jobs.

The more he struggled, the more he missed his family in the North, especially his son. He saved $4,500 and, using intermediaries because no banking transfers are allowed between North and South, sent it to his ex-wife in the North, who told him that she wanted to be reunited. He also felt guilty for leaving home after he learned that his father had died while he was away. To add to his woes, the broker who smuggled him from China to Thailand sued him, accusing him of not paying all of his fee.

Then in May last year, Mr. Kwon said, he finally “snapped.” When he didn’t get the pay he said he had been promised for carrying bricks, he asked the police to intervene, but they sided with his South Korean boss, who denied Mr. Kwon’s accusation.

“I will go back to the North and hold a news conference there to tell the truth about what the life was like in the South,” he yelled at them, according to court records.