Eight men have been arrested in connection with an October robbery in the suburban Tokyo city of Inagi, police said Thursday, as officers attempt to track down the "Luffy" ringleader suspected to be behind a spate of burglaries across the country.

Japan has been rocked by the robberies, which began last year and appear to be carried out by people instructed by ringleaders using the encrypted messaging app Telegram. Among the cases is the murder-robbery of 90-year-old Kinuyo Oshio in her home in the city of Komae in Tokyo on Jan. 19.

In the Inagi case, the police believe the suspects colluded in forcefully entering a residence, injuring a resident and stealing gold bullion and other valuables and some 35 million yen ($271,000) in cash. One of the eight has been released pending a decision.

Analysis of phones belonging to some of the arrested show they received instructions from three names -- Luffy, Kim and Mitsuhashi. The telephone number linked to Luffy suggests the person is in the Philippines, the police said.

Police officers investigate the scene of a suspected robbery-murder incident in the suburban Tokyo city of Komae on Jan. 25, 2023. (Kyodo)

According to the police, the majority of those arrested appear to have been recruited online. One suspect has reportedly told officers that he "told them about me and my family, and I couldn't get out of it because I was afraid my family would be hurt."

Some of the eight are linked to other incidents believed to have been the group's work, with three of them previously indicted for an attempted robbery in Iwakuni, Yamaguchi Prefecture, in November last year.

Two are suspected to have been involved in an attempted murder and robbery in Hiroshima and a robbery causing injury in Tokyo's Nakano Ward, both in December.

Speaking at a regular press conference on Thursday, the National Police Agency's Commissioner General Yasuhiro Tsuyuki said that "uncovering the identity of the ringleader and cracking down on them are important."

He added that the agency will hold a meeting on the investigation Friday to be attended by senior officers including the head of its organized crime department.

In the investigation of the robbery that led to Oshio's death, the phone of alleged group member Rikuto Nagata, 21, who was arrested Saturday on suspicion of involvement in the Nakano Ward robbery, was found with messages from the presumed mastermind pertaining to the incident.

In response to reports of a suspicious vehicle in Tokyo's Adachi Ward, police on Friday found a rental car with the same license plate as one seen fleeing the vicinity of Oshio's home, and arrested Nagata the next day.

A smartphone found inside the rental car not only contained correspondence related to Komae, but also several addresses in Adachi Ward, suggesting the group planned to stage further attacks. A luxury brand watch believed to have been stolen from Oshio's home was also found in the car.

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