An 18-year-old male high school student was arrested Saturday for allegedly connecting a boy, 16, with other alleged perpetrators of a high-profile robbery-murder case in Tochigi Prefecture.

In the case, Eiko Tomiyama, 69, was killed at her home in the town of Kaminokawa on May 14.?

The 16-year-old boy, a high school student from Kawasaki, and three other male high school students, all 16, had been arrested by the Tochigi Prefectural Police by May 16. Police suspect they were the perpetrators of the crime.

Around May 13, the 18-year-old student arrested by the Tochigi police Saturday, who is from Sagamihara, Kanagawa Prefecture, allegedly introduced the Kawasaki boy via a communication app to one of the other three boys who played a leading role among the assailants, despite knowing that the Kawasaki boy would be a perpetrator in the robbery.

The 18-year-old boy is suspected of violating the employment security law, which bans the introduction of harmful jobs.

The police have identified Kazuhiko Masuda, 48, as the key suspect who orchestrated the robbery, and Kaito Takemae, 28, and his wife,?Miyuu, as the on-site supervisors.

Masuda left Japan from Narita International Airport in Chiba Prefecture for China following the arrest of Takemae, investigative sources have said. The man may have traveled to Southeast Asia or another country after arriving in China.

The Tochigi case involving ³Ù´Ç°ì³Ü°ù²â¨± quasi-gangster groups is highlighting how the groups are adapting to police crackdowns.

Police believe there might have been involvement by senior members of ³Ù´Ç°ì³Ü°ù²â¨± groups, which thrive on anonymity and a lack of structure, in orchestrating the plot.