The suspected "Luffy" mastermind and three others believed to be behind a string of Japan robberies and now in detention in the Philippines appear to be senior members of a fraud group from which 36 members were detained in the country in 2019, an investigative source said Saturday.

Police have requested the transfer of the four men to Japan from Manila, after obtaining arrest warrants on suspicion of theft in relation to the fraud, which targeted elderly people in Japan. The suspects named in the arrest warrants include Yuki Watanabe and Kiyoto Imamura.

The four are believed to be behind a spate of robberies starting last year that used similar tactics to the fraud operation, including offering large payouts to individuals recruited to stage the crimes.