A series of robberies across Japan that have been linked to so-called yami baito (“dark” part-time jobs) reached a new level of attention after a group of mask-wearing teenagers were caught on video robbing a store in broad daylight in Tokyo's Ginza district earlier this month. The crime was initially thought to be linked to the recruitment practice.

However, it emerged on Thursday that three of the four suspects arrested over the Ginza robbery already knew each other, indicating that they were not independently recruited for the heist using social media.

Criminal activities carried out by young people who are recruited through yami baito job postings have become a major issue, with the Japanese police on high alert amid calls for cyber patrols and stronger preventative measures.