The leader of a Telegram sex crime ring which facilitated the exchange of thousands of sexual abuse materials has been sentenced to life imprisonment in South Korea.

Kim Nok-wan, 33, was the head of the so-called Vigilantes: a large-scale, pyramid-style group that blackmailed victims into producing explicit content and sharing it in online chatrooms.

Between May 2020 and January 2025, the Vigilantes exploited at least 261 individuals – the largest number of cybersex exploitation victims in South Korea's history.

Under the self-designated title of "pastor", Kim was found to have carried out systematic crimes including the sexual assault of minors and the distribution of images that show child sex abuse.

He was sentenced on Monday after being convicted for organising and operating a criminal organisation, producing and distributing sexually exploitative and illegally filmed material, forcing the use of illegally filmed material, and "quasi-rape" or sexual assault where the victim was unable to resist.

"[Kim Nok-wan] says in court that he is remorseful, but he committed countless crimes over the past four to five years," the court said.

"Considering the brutality of the crimes and the lack of restitution for victims, it is necessary to permanently isolate him from society."

Kim sought out both male and female targets through social networking platforms, luring them to the instant-messaging service Telegram before blackmailing them, according to police.

He approached men who expressed interest in creating or distributing deepfake images, and women who expressed sexual curiosity, then threatened to disclose their personal information or report them to authorities.

Some of these victims would subsequently be recruited into the Vigilantes pyramid scheme – allocated titles such as "evangelist" and "deacon" - so that they could bring in further victims.

Kim ordered both adult and child victims to submit "hourly daily reports" and write letters of remorse, punishing those who failed to do so by forcing them to take nude photographs or harm themselves.

The quantity of sexually exploitative materials produced by the Vigilantes exceeded 2,000 pieces of media.

As its ringleader, Kim also raped ten under-aged women, forced women to have sexual intercourse with other men and filmed himself committing brutal acts that caused injury, police added.

He was found to have participated in at least 453 Telegram channels and chat rooms for the purpose of committing his crimes - 60 of which he operated personally.

The case marks the first time Telegram has cooperated with South Korean police, providing crime-related data that facilitated further investigations and led to Kim's arrest.

The Korean National Police Agency established a formal system of investigative cooperation with Telegram in October 2024, enabling the platform to officially provide authorities with relevant information.