The Tachikawa branch of Tokyo District Court on Thursday handed down an indefinite prison term to a 23-year-old man for his involvement in a total of six robberies in four Japanese prefectures in recent years, including one in which a 90-year-old woman was fatally assaulted.

According to the ruling, Rikuto Nagata was involved in the six robberies, which occurred between November 2022 and January 2023 in Tokyo and the nearby prefectures of Chiba and Kanagawa, as well as the western prefecture of Hiroshima.

The cases are part of a series of high-profile robberies across the country that are believed to have been masterminded by ringleaders who went by names including "Luffy."

In one of the six cases, Nagata was found to have conspired with other perpetrators to fatally assault the elderly woman in the Tokyo suburb of Komae on Jan. 19, 2023, and take four items worth a total of about ¥590,000, including a luxury watch.

Nagata was indicted on charges including robbery resulting in death. The indefinite prison sentence came as sought by the prosecution.

At the court branch on Thursday, presiding judge Akira Sugawara said Nagata was involved in "a brutal crime that could be called torture."

The judge pointed out that Nagata led the group of perpetrators at the scene, instructing another perpetrator to beat the woman with a crowbar, while he himself attacked her. Nagata's responsibility was "remarkably heavy," the judge added.

After handing down the sentence, the judge told Nagata, "I want you to continue to think about what you can do to make amends, while serving your sentence." Nagata was seen wiping his eyes on his sleeve.

In the Komae case, Issei Nakanishi, 21, who was one of the perpetrators, was sentenced to 23 years in prison in September. Three others have also been indicted, including Yuki Watanabe, 40, a leader of a special fraud group who allegedly directed the robbery.