A man in his 40s who allegedly masterminded a recent robbery-murder in Tochigi Prefecture left Japan from Narita International Airport in Chiba Prefecture for China following the arrest of another person involved in the case, investigative sources said Thursday.

Investigators found that the man, for whom an arrest warrant has been issued, was an acquaintance of Kaito Takemae, 28, who was arrested on suspicion of instructing 16-year-old boys to carry out the robbery-murder. They also said the man prepared a crowbar for use in the robbery.

Tochigi Prefectural Police are investigating his whereabouts, suspecting that the man may have fled abroad from a different airport than planned after learning that Takemae was arrested shortly before departing Japan from Tokyo¡¯s Haneda Airport. They are also investigating the possible involvement of a ³Ù´Ç°ì³Ü°ù²â¨± anonymous and fluid criminal group.

The man is suspected of conspiring with Takemae, his wife, Miyu, 25, and four 16-year-old boys, who broke into the home of Eiko Tomiyama, 69, in the town of Kaminokawa and killed her on the morning of May 14. The wife and the four boys have also been arrested.

Kaito Takemae was arrested on May 17 just before boarding a plane bound for Seoul. According to investigative sources, an analysis of Takemae¡¯s seized smartphone revealed that the man gave instructions through a highly anonymous app.

The man bought the crowbar at a hardware store in Kanagawa Prefecture and handed the weapon to Takemae before the incident. He was found to have left for China via Narita International Airport within a few days of Takemae¡¯s arrest, according to the sources.

The man may have traveled to Southeast Asia or another country after arriving in China, as Takemae had intended to go to Manila via Seoul, they said.