Won Eun-ji was working on her laptop in a cafe when she clicked on a video so horrifying that she slammed the screen shut again.
The university student had been investigating a disturbing network of online chatrooms, where thousands of men would pay for access to photos and videos of women and girls coerced into performing sexually explicit and depraved acts.
The victims were as young as 12.
Eun-ji had been exposed to the footage on an almost daily basis since she began looking into the chatrooms with her classmate, Park Ji-hyun in 2018.
But this particular video seared into her memory.
A teenager was using a knife to engrave the word "slave" onto her body.
"I couldn't believe it," Eun-ji said.
"I was so surprised that I got goosebumps all over my body and closed my laptop right away."
What began as part of an online journalism competition snowballed into an all-consuming project for the students who, together, adopted the moniker "Team Flame".
Their work set in motion what would become a major police and media investigation into the largest and most infamous case of digital sexual slavery in South Korea.
A pair of young men who facilitated the network would eventually be caught and sentenced to more than 30 years' jail, and a slew of other offenders were caught.
But to get there, Eun-ji had to spend months immersed in a digital world of sexual torture that continues to haunt her years later.
Uncovering disturbing sex crimes in the 'Nth Room'
Eun-ji and Ji-hyun had intended to write about Korea's spy camera epidemic, where men use hidden cameras to secretly film women in private moments, in public restrooms, hotels and changing rooms.
The pair found a chatroom on the encrypted messaging service Telegram, where they made a shocking discovery.
Rather than depicting victims who were unaware they were being filmed, these videos showed women and girls who had been blackmailed into providing sexually explicit videos and photos.
What was known as the Nth Room was actually a series of eight chatrooms: the more a user paid, the more depraved the material. The admin was a member called "Godgod".
Another user who called themselves "Baksa" — the Korean word for doctor — ran the Baksa Room.
Women and girls were lured into the chatrooms with promises of earning lucrative modelling contracts.
After the admins obtained personal details and some suggestive photos from their victims, they would then start to demand increasingly graphic and dehumanising content.
There were threats to expose victims to their peers, family, work or school. Those who remained uncooperative would have their details posted in the chatrooms, where members would threaten them with rape.
Eun-ji was struck by how unashamed the abusers were, seemingly devoid of any guilt or remorse, despite the torment they were inflicting.
"They treated women, children and adolescents like products, not human beings," Eun-ji said.
"They had a conversation about treating women as objects, referring to body parts, saying, 'it looks delicious', 'I want to eat it'.
"They also said things like, 'If you feel like dying because the video spreads, give it to me before you die.'"
Team Flame infiltrated any chatrooms they could, gleaning information about the perpetrators, and handing it on to police.
Eun-ji recalled how she acted like the perpetrators to gain their trust.
"I changed my way of chatting to look like I shared the same online culture as them," she said.
"They're criminals and I had to call them big brother.
"That was the hardest part. I'm still undergoing psychiatric treatment."
Eun-ji eventually helped to secure the conviction of at least two perpetrators, "Rabbit" and "Callie".
But these were relatively low-level users. It was clear the problem was much bigger than she could handle alone.
"There were more than 1,000 people in the room where I first infiltrated," she said.
"But three months later, it already increased to more than 5,000."
Ringleaders retaliate with further abuse, doxxing reporters
Eun-ji and Ji-hyun's report won the university competition, and caught the attention of journalists Oh Yeon-seo and Kim Wan, from daily newspaper The Hankyoreh.
The investigative journalists connected with Team Flame and gained access to the chatrooms.
"[Eun-ji and Ji-hyun] went beyond the boundaries of journalists a little more and went into the room and captured evidence like a police detective to [try to] actually solve this case," Yeon-seo said.
"I wondered if they were students, reporters or detectives. I thought they were great."
In November 2019, the newspaper published their joint investigation on the front page, under the byline "specialist coverage team" as a layer of security for those working on the story.
The Hankyoreh published several subsequent reports, but to their great surprise, the nation's media initially paid little attention.
"It seems that people thought it was just one of the digital sex crimes that have always happened in South Korean society," Yeon-seo said.
"The reason why such crimes were so prevalent was that our society took such crimes too lightly."
But those behind the sexual exploitation were furious.
Their chatroom members targeted Kim Wan after initial, surface-level reports included his name in the byline.
"When he first reported the room to society, [chatroom members] said, 'Let's find out his personal information'," Yeon-seo said.
"Some even said they would give free illegal sexual exploitation videos if someone brought personal information such as the names of his family, the number of children and what articles he was writing."
The ringleader, Baksa, unleashed a barrage of never-seen-before images of sexually exploited women, along with threats against the newspaper.
"He said that this child is a victim of Hankyoreh," Yeon-seo said.
"He kept posting photos and videos with the logic that the more Hankyoreh reports, the more victims he will continue to create.
"It was at this time when my colleague and I seriously thought about whether we could handle this. We were seriously concerned about whether [our reporting] could be justified, no matter what good we were doing this for."
It was one of several tactics Baksa used to try to stop other news outlets from investigating or bringing attention to the chatrooms.
Two major current affairs television programs picked up the story.
Baksa tried to cut deals with journalists and, at one stage, threatened to force an exploited victim to throw herself off the TV studio's building if a program exposing the crimes went ahead.
A familiar phone scam foils the plot
As the media attention increased, police tracked down more victims and closed in on the perpetrators.
The big breakthrough came once police established that the ringleaders had used mules to collect payments and "drop" money at a specific location for collection.
It was a unique style of payment and had been used for a familiar phone scam.
"It made us think [Baksa] could have been involved in phone scams as well," senior inspector Cho Seung-noh told the Netflix documentary, Cyber Hell: Exposing an Internet Horror, released earlier this year.
The hunch was correct.
Court documents showed one of Baksa's usernames had been used in a scam, and police began watching a fire hydrant where the scammers' mules would regularly drop off cash for collection.
In March 2020, they swooped.
Waiting for the criminal to leave his house so that he would be unable to delete evidence in the midst of a raid, they took their chance when he returned from a bike riding lesson with his father.
Baksa was revealed to be 24-year-old Cho Ju-bin.
His accomplice, Moon Hyung Wook — or Godgod — was arrested in May.
Officers made an exception to the longstanding South Korean custom of protecting criminals' identities, after millions signed a petition demanding anonymity be lifted.
Cho Ju-bin was paraded in front of media outside a Seoul police station.
"Thank you for stopping a life of a devil which I couldn't stop myself," he said.
The 'beginning of the end', or just the tip of the iceberg?
South Korea was deeply rattled by the extent of the abuse exposed in the chatrooms.
At least 103 women, including 26 teenagers, were identified as having been forced into providing sexual material that was distributed to some 60,000 chatroom members.
Cho Ju-bin received a 40-year sentence, while his offsider, Moon Hyung Wook, was jailed for 34 years.
By the end of 2020, 3,757 people had been arrested, according to the Netflix documentary.
The investigation was touted as the "beginning of the end" for these chatrooms, but activists warn sexual exploitation is continuing to grow.
In November, a joint operation between South Korean and Australian police arrested a man in Sydney, known as "L".
He is accused of forcing at least nine underage victims into providing sexually exploitative material, which was then shared in as many as 30 Telegram chatrooms, Yonhap News Agency reported.
The operation was dubbed the "second Nth Room".
Since the Nth Room case, reports of online sexual exploitation have increased by 60 per cent, according to Cho Jin-kyung, who runs the Centre for Teenage Women's Human Rights.
Jin-Kyung said that, while this could be partly attributed to increased reporting and police action, the type of crime was also happening more frequently.
"When the victims came to our institution or tried to report it to the police, they were afraid that they, as the victim, would be responsible because they took a picture of themselves and sent it," she said.
South Korea has passed so-called "anti-Nth Room" laws that strengthen punishment for these crimes, including looking at or possessing such material.
Underage victims are no longer questioned as to whether they sent images "voluntarily".
"This is a very important law. The problem is that, even though the law has changed, the social perception that if it is 'voluntary', the victim is still responsible," Jin-Kyung said.
Internet providers are also compelled to stop their systems from being used as carriers, but Google has been accused of being too slow to respond to victim complaints.
Telegram, which does not have servers in South Korea, is not subject to the anti-Nth Room laws and has so far refused to cooperate with police, according to The Korea Herald.
South Korea also has a history of handing down "soft" punishments for sexual crimes.
The law allows alleged perpetrators to rely on intoxication as a defence to mitigate responsibility for sexual crimes, including rape.
In 2019, a South Korean man named Son Jong-woo was sentenced to 18 months in prison for running one of the biggest known child pornography websites.
He is now serving an extra two years — more time than his original sentence — for hiding the proceeds of crime.
South Korea refused to extradite him to the United States, where some of the website's users were sentenced to between five and 15 years in prison.
In 2020, K-Pop star Jung Joon-young had his six-year sentence reduced to five, for the gang rape of two different victims in 2016.
He also shared spy cam footage of him having sex with another woman.
"Two years have passed since the law was changed, and there have been very backward rulings over the past two years," Jin-Kyung said.
The reporters who uncovered the crime fear repercussions
Journalist Oh Yeon-seo says despite the increased police attention and changes in the law, she fears online sexual exploitation in South Korea will never end.
"To be very cold-headed, I don't think this can end," she said.
"We have taken this crime lightly for too long, and it is still difficult to investigate."
She worries about what will happen when the Nth Room ringleaders are eventually released.
"When he's released, won't he retaliate against us?" she said.
It's a fear Won Eun-ji shares. It was only recently that she agreed to having her name published in relation to the work she has done. But she still wants her image to stay private.
"I don't feel safe. I'm afraid of retaliation," she said.
Along with her fellow Team Flame investigator, Park Ji-hyun, she is continuing her work to advocate against sex crimes in South Korea.
"I have to meet people and listen to them as a journalist, so I'm using my real name to give them more trust," Eun-ji said.
