Such rooms, each measuring 3 sq m by 6 sq m, started out in the 1980s as cheap, short-term accommodation for students cramming for examinations, but have become associated with the destitute and poor, and a growing number of South Koreans who are priced out of the property market.

But the 26-year-old was not in dire financial straits, according to South Korean media reports.

Known for her bubbly and cheerful image, she had made a name for herself after appearing in variety and reality shows on South Korean TV. She even has a fan club which threw a birthday party for her in April.

She moved from Namyangju on the outskirts of Seoul to the capital's affluent Gangnam district in January. JoongAng Ilbo newspaper, citing sources, said her living space - albeit tiny - was well kept.

Her friends and acquaintances said all her belongings in her residence in Gangnam remained untouched, reported Korea Herald.

"If she went back voluntarily, she would have taken care of her assets here, but most of it seems untouched," lawmaker Cheong Yang Seog from the Bareun Party told a meeting last Tuesday.

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In her tearful confession aired on North Korea's state-run website Uriminzokkiri last Sunday, Ms Im said she had "returned on her own will". But there is widespread scepticism that Ms Im - or Jeon Hye Sung, as she was known in the North - had returned voluntarily.

In fact, things were looking good for her just before her disappearance in April. She said in a blog post that she would get busier soon because she had just enrolled in a school. And in a message to her official fan club in April, she thanked fans for throwing her a birthday party, writing that it was probably the "happiest birthday of my life".

Some experts and defectors said it was highly likely she was the target of a state-sponsored abduction. "Experts are carefully suggesting that Im had become a target of the North Korean State Security Department," said Mr Cheong.

In the 27-minute clip, Ms Im was introduced as Jeon Hye Sung.

"Im Ji Hyun" is believed to be an alias given to her as part of Seoul's defector protection programme.

Scrutinising her latest appearance, some netizens commented that Ms Im's eyes looked swollen from crying, her cheeks were puffy, probably from beating, and that make-up had been piled on her face to cover the puffiness. She was among the top searches on South Korea's widely popular Naver Web portal in the past week.

Mr Cheong said that Ms Im may have disappeared in April when she was visiting China for "shopping and business" on a South Korean passport.

Ms Im was granted citizenship in the South after clearing extensive background checks by intelligence officials upon her arrival in the South in January 2014. Such measures are intended to prevent spies, criminals or ethnic Koreans pretending to be from the North from entering the country.

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Local media said the North Korean regime may have begun to notice Ms Im after she appeared on a South Korean television show where she showed off her singing skills and spoke about her life in North Korea.

An unnamed source, who is familiar with Ms Im's case, told JoongAng Ilbo that it is highly likely the North had abducted her to serve its propaganda objectives.

In the recent video clip, Ms Im was dressed in a traditional hanbok and wearing a red badge featuring images of former leaders Kim Il Sung and Kim Jong Il.

She told viewers she regretted escaping to the South. "I thought I could eat well and make a lot of money in South Korea, but every day was like hell there," she said, urging other defectors in South Korea to return to the North.

"Let's return to our motherland and see our parents' faces before we die," she said, adding that she is staying with her parents in the western city of Anju in North Korea's South Pyongan province.

She blasted the capitalist South where "everything is judged by money". "I imagined myself eating well and making a fortune once I arrived in South Korea," Ms Im said in the interview, "but after going around to different places including bars to earn money, I came to realise life was physically and emotionally taxing."

Ms Im added that she had been forced to make the North look bad in her TV appearances. "Everything I said on TV was scripted to make North Koreans look barbaric, ignorant and stupid. I had no other choice but to say whatever they wrote in the script, and at one time I was told, 'You think it's easy to earn 400,000 won(S$488)?'"

The broadcaster, TV Chosun, has adamantly denied her charges.

Since December last year, she had been a regular guest on Moranbong Club, a talk show where guests would denounce the Kim Jong Un leadership - a crime punishable by death back home. She had also starred in a reality dating show, South Korean Men And North Korean Women.

Another defector-turned-TV celebrity, Lee So Yul, defended Ms Im's actions. She said Ms Im's facial expression in the video was that of a person "begging to stay alive". "She has no choice in order to survive," Ms Lee said in a YouTube broadcast.

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Police trying to trace route of re-entry

South Korean police are analysing data on Ms Im Ji Hyun's personal phone records and financial transaction records to try to map out the route she took to re-enter North Korea.

The police are also looking into whether she has broken national security laws, according to local media.

Ms Im spent three years in China before defecting to the South in 2014, according to Korea Herald. Police reports showed she left behind a Chinese husband and she reportedly made frequent trips to China to see him.

It is also not uncommon for North Korean defectors to hire brokers to reunite them with their North Korean family members at the North Korea-China border, or even try to smuggle them out of the country - a risky move as North Korea has stepped up security on its border with China in recent years. A number of them ended up being caught by the North Korean agents.

Ms Im's puzzling reappearance across the border has led to calls from some defectors for better protection by South Korean authorities. Around 700 police officers are tasked to look after more than 30,000 defectors who have fled to the South since the 1990s. The police, according to the Korea Times, group the defectors into three categories based on their profiles, careers and social backgrounds in the North.

Most belong to the third and lowest category and rarely receive police attention once they complete six months of training to assimilate into the South Korean society, the sources said.

Ms Im belonged to the third category.

But Mr An Chan Il, a defector- turned-researcher who heads the World Institute for North Korea Studies in Seoul, said defectors in the South should be self-reliant and be responsible for their own safety.

"There are too many of us and the police can't take care of each one," he was quoted as saying by Korea Times. "Moreover, some defectors see it as infringement of human rights if police officers contact them."

South Korea's Unification Ministry, which handles inter-Korean relations, said it did not know exactly how many defectors in total returned to the North. It said 25 North Korean defectors have made similar television appearances in the North in the past five years. Among them, five fled to the South again, including one North Korean man this year, reported South Korean daily JoongAng Ilbo.