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Back in May, a young Thai woman walked into a supermarket in Busan around 4:20 a.m and cautiously handed a note to the cashier Kim (27). 

In the note was a message in English, Korean, and Thai. The woman claimed that she has been trapped on the fourth floor of a building and was ''illegally working''. 

The cashier suggested help and responded on the note, "Do you want me to call 112 (emergency services)?" The woman, who had several suspicious men with her at the time, rejected the idea in fear of getting caught. Instead, the cashier received a phone number from her while pretending to be needing the number for the supermarket's point reward system. 

After the woman left, the cashier reported the note to the police around 8:30 a.m. The police started investigating the buildings around the supermarket but faced difficulties as the note did not include specific details. 

However, the phone number on the note provided more clues as it matched with the number of Lee (38), who has previously been booked for running a prostitution establishment 'Kiss Room'.

A post on Facebook by a friend of the Thai woman also greatly helped the investigation. The post included a photo of the secret note and stated that her friend is locked up and has been forced into prostitution in Busan. 

With the evidence, the police immediately rushed to a speculated building in Busan, where they were able to arrest Lee and 4 other men. In the building were 5 Thai women who were forced into prostitution. 

Police revealed that Lee was introduced to the 5 Thai women by a broker Kim (40) back in January. He had the women locked up in the building from March to May and ran a prostitution business. Lee revealed to have received 100,000 KRW (~86 USD) per session. However, the Thai women did not receive any payments in the first month and were only given 40,000 KRW (~35 USD) in the second month per session.

The police have also booked 53 Johns who were engaged in prostitution. Currently, the investigation is ongoing with about 300 other men who are suspected to have used the prostitution establishment.