Earlier this year, one of the most prominent North Korean defectors, Yoo Woo-sung, walked out of his apartment building here and found four South Korean government vehicles waiting for him.

Authorities hauled Yoo away and arrested him on charges of espionage. They had learned of his alleged crime, court documents show, thanks to testimony from his sister, who said Yoo had been sent on a mission by North Korea’s secret police to infiltrate the defector community and pass back information about the people he met.

Yoo, 32, is being held at a detention center on the outskirts of Seoul, his case a reminder of how this peninsula’s messy and sometimes covert conflict has left the South on edge, with people here unsure whom they can trust.

Defectors from the North are increasingly facing the brunt of this suspicion. As more flee to the South — some 25,000 in total, nearly all coming in the past two decades — South Korean analysts and government officials say the North has expanded a program used to sow anxiety and collect information, both by disguising spies as defectors and by pressuring defectors to become spies after they arrive. The South, in turn, has raised its guard about those entering the country, changing its protocol three years ago to allow for lengthier interrogations of arrivals from the North.

Yoo’s trial, which began May 9 and could continue for weeks, weighs two conflicting scenarios. In the first, argued by prosecutors, Yoo was threatened by the North into serving as a spy. In the other, put forward by the defense, Yoo is an innocent defector whose sister — after attempting her own defection to the South in October — was coerced into a wrongful confession by intelligence agents who interrogated her for more than two months and then held her in near-solitude for several months more.

The account of Yoo’s case — based on an extensive review of legal documents, as well as interviews with Yoo, his attorneys, his sister and his former colleagues, acquaintances and roommates — casts new light on the way defectors are treated when they arrive in the South and after they settle. A brief statement about the interrogation tactics was provided by South Korea’s National Intelligence Service (NIS), which led the investigation of Yoo’s sister. South Korean prosecutors by custom do not speak with the media before a trial and declined several requests.

In the past five years, South Korea has arrested 14 defectors accused of being spies — something previously unheard of — and Yoo is perhaps the highest-profile among them. Before his arrest, Yoo was working at City Hall as the first defector to become a Seoul city servant, and he occasionally visited elementary and high schools, speaking about his frustration with the North’s government and expressing hope for Korean unification. Soon after Yoo’s arrest Jan. 10, the South said it would strengthen background checks for defectors who apply for public-sector jobs.

Yoo maintains his innocence and said in a recent interview at the Seoul Detention Center that he feels “totally helpless.”

Sitting behind a clear plastic pane that divides the room where he can meet with outsiders for 10 minutes daily, he wore an olive jumpsuit bearing his prisoner number, 50. Yoo spoke in a rush, occasionally using fragmented English.

“I don’t know why my sister has done this,” he said.

Those who know Yoo in South Korea say that if he was a spy, he hid it extremely well. He stood out for only one reason: Compared with many defectors bewildered by the capitalist and high-pressure South, Yoo, who arrived in 2004, adjusted unusually well to the free world. He earned a degree from Yonsei, one of Seoul’s top universities, and packed his days with social activities — speaking engagements, dinner parties, weddings, weekly meetings with four or five defector groups.

Yoo was hired at City Hall in 2011, and the job suited him well, friends and colleagues say. He assisted those in need of Seoul’s welfare programs, including many defectors. One day, a network television camera followed him on the job as he visited an elderly defector confused by tax documents.

“Defectors trust me more because I understand them better,” Yoo said as the camera rolled.

But Yoo was different from most defectors — and he defected successfully to South Korea only because he kept a secret when he first arrived, Yoo’s attorneys now admit. He had indeed been born in North Korea, but he was a Chinese citizen — meaning he carried a Chinese passport and could enter and exit the North with freedom inconceivable to the average North Korean. That Yoo held a Chinese passport was an important detail, because Chinese — even those born in the North — are not entitled to automatic South Korean citizenship, as are typical defectors. Yoo’s attorneys say Yoo lied to interrogators about his identity when he arrived, and he received years of aid, earmarked for defectors, to which he was not entitled.

There are some 4,000 Chinese in the North, living in pockets in Pyongyang or, as Yoo’s family did, along the northwestern border. His father was a city worker and his mother a nurse; both were born in China. When they ran low on food, Yoo was able to cross into China and earn money by selling deer meat, mushrooms and North Korean-made pottery.

Still, after Yoo arrived in the South, he gave friends here the impression his family was no different than others in North Korea, something that has become a point of bitterness and suspicion for other defectors. He spoke about his family as many defectors do — sparingly but with concern. He did occasionally express hope about reuniting with his only sister, younger by seven years. But Yoo never mentioned that she had moved from North Korea — where she, too, had been born and raised — to China in 2011.

Yoo, like some higher-profile defectors, also kept in touch with a member of South Korea’s NIS who served as a de facto minder. When his sister, Yoo Ga-ryeo, set out for South Korea on Oct. 30, Yoo sent a hopeful text message to the NIS agent. Yoo did not mention that his sister’s defection would require the same deception he had used.

“She’s my only sister,” Yoo told the agent, in a message shared by Yoo’s attorneys. “Please look out for her.”

“Everything will work out,” the agent replied.

A stark choice

As with any new defector, Yoo Ga-ryeo’s first stop in South Korea was the Joint Interrogation Center in Gyeonggi province, outside Seoul. The facility, activists say, is a legal gray zone where defectors are given no guidance from lawyers, allowed little sleep, interrogated at odd hours of the night and sometimes kept in solitude for weeks at a time.

It is here that South Korean intelligence officials try to weed out spies.

The 14 defectors arrested over the past five years compare with zero in the five years prior. According to South Korean officials, they include would-be assassins as well as a temptress who tried to extract secrets from military officers. Among those defectors charged with espionage, at least one has been acquitted.

Fueled by concerns about the arrests, South Korea enacted a law in 2010 that allowed new arrivals to be held and interrogated for up to 180 days. Previously, interrogations had been capped at 90 days.

For Yoo Ga-ryeo, the tone of the interrogation intensified after agents realized she was a Chinese citizen, she later said.

According to documents from prosecutors, Yoo Ga-ryeo was then asked about her brother. It is unclear whether those agents had previous reason to suspect him of wrongdoing, but the NIS said in a statement that the subsequent investigation of Yoo Woo-sung “originated” from what Yoo Ga-ryeo said next. It was a story she would retract.

She said her brother had initially settled in the South with no intention of working on behalf of the North. But that changed when he took a risky trip back to the North in 2006, bribing his way across the Chinese-North Korean border to attend their mother’s funeral, she said.

Days after the funeral, she said, her brother was dragged away by North Korea’s secret police, the Bowibu, for seven days of investigation. After that, she said, Yoo walked with a limp from the beatings he had received. He had also been given a stark choice: He could return to the South, burrow into the defector community and report back about those whom North Korea describes as “human scum,” or his family would be imprisoned.

The sister told agents that Yoo agreed to work for the secret police.

And she said she was complicit in his plot.

Yoo returned to South Korea, where he met hundreds of defectors, recording their names and contact information, Yoo ­Ga-ryeo told her interrogators. He then sent files on some 200 people to North Korea with her help, she said — she would cross from North Korea into China, download the data at an Internet cafe near the border and then carry the information back to the North. Yoo Ga-ryeo also testified that her brother, between 2007 and 2012, took several secret trips to North Korea to meet with the Bowibu.

After Yoo Ga-ryeo told all this to the South Korean intelligence agents, prosecutors decided that her testimony should be made part of the official record.

So on March 4, Yoo Ga-ryeo was taken to a district court, where prosecutors asked her more than 140 questions, according to a court transcript, and where she restated the case against her brother, who was also in the courtroom.

“You and your brother work for the Bowibu?” she was asked.

Yes, she said, sobbing.

“You’re afraid of some kind of revenge from them, so that’s why you decided to work for them?”


Recanted story

But last month, Yoo Ga-ryeo changed her tone, a shift that came after she encountered her brother in a courtroom for a second time.

Their meeting came during an April 26 hearing, at which a judge would rule whether Yoo Ga-ryeo was being illegally detained at the Joint Interrogation Center. At that point, she had spent 178 days with the intelligence agents.

It was springtime, but Yoo ­Ga-ryeo arrived in court wearing a heavy green hooded jacket, her skin pasty, her eyes red, her hair in a bun. Her brother walked in minutes later; he had come to help petition for her release. He was handcuffed and bound by blue rope around the waist.

Guards removed the rope and cuffs, and Yoo sat one row in front of his sister.

He looked back at her once, tentatively. She began to sob.

He looked back again seconds later, and his voice squeaked: “Don’t worry. I’ll save you.”

He reached out his hand toward her. She rose from her chair, lunged for it and fell to the floor, her body heaving with sobs.

An hour later, a judge ruled that Yoo Ga-ryeo was free to leave the interrogation center but that she would be deported to China by May 23. She spent the next morning with Yoo’s attorneys, who called a small news conference at their office in the Seoul neighborhood of Gangnam.

There, Yoo Ga-ryeo said that everything she had told agents about her brother was false. Her brother was not a spy, she said, and they had never worked with the Bowibu.

She said her original story was simply a way to make agents stop mistreating her. Those six agents had kicked her and hit her in the head, she said. They also misled her, she said, making her believe Yoo had confessed to spying. The agents told her that she would be rewarded — and that her brother would be given leniency — if she cooperated and confirmed their suspicions.

Those agents then drafted a confession for Yoo Ga-ryeo — one filled with details that laid out Yoo’s double life.

“I copied [the confession] with my own handwriting and signed it,” Yoo Ga-ryeo said.

“I’m really sorry for what I have done to my brother,” she added. “I made him suffer.”

South Korean authorities say Yoo Ga-ryeo’s news conference retraction will not change their case against her brother. Her initial testimony, they say, is part of the official legal record. They said they believe it is true.

“Her change of the testimony was coerced by the lawyers,” one official at the prosecutor’s office said in a brief conversation before declining an interview.

The intelligence service, in its statement, said it uncovered additional evidence of Yoo’s spying after a search of his apartment and office, but it declined to specify its findings. The NIS says it has also found witnesses who spotted Yoo on trips to the North. The NIS denied using violence against Yoo Ga-ryeo during her interrogation.

But Yoo’s attorneys say that the additional evidence against Yoo is spotty at best and that the court should not rely on the years-old memories of witnesses. They say authorities have found no evidence on Yoo’s computer that he sent files or names to his sister.

They say the case hinges, instead, on the testimony of a sibling who was easy to manipulate and relying on a skill that served her well in the authoritarian North: She will say what it takes to please authorities.

“When she confessed, a lot of people questioned why she would testify against her brother,” said Jang Kyung-uk, the senior lawyer representing Yoo. “But maybe this is a lesson, because a lot of people don’t know what defectors go through during interrogation. They are not briefed on their rights, and they are kept in solitude. Human nature is to get out of that process as quickly as possible.”

Yoonjung Seo contributed to this report.