Investigative sources say police suspect that a person using the name "Luffy" was the mastermind behind a spate of robberies in Japan.

Police suspect that the robberies were carried out by groups of people who had been recruited through social media. They allegedly broke into homes and shops in accordance with Luffy's instructions.

The sources say analyses of phone records of arrested suspects suggest that Luffy was involved in robberies that occurred in Kyoto, Tokyo's Inagi City and Hiroshima last year.

In the Kyoto case in May, luxury watches worth over 500,000 dollars were stolen.

The sources say the instructions were likely sent from overseas through an app that allows users to send messages that self-destruct after a certain period of time.

Police suspect that the same system may have also been used in robberies in Shiga, Osaka and Yamaguchi prefectures.

In a suspected robbery and murder case, a 90-year-old woman was found dead in her house in Tokyo's Komae City earlier this month.

Messages that appeared to be related to this case were found on the mobile phones of suspects arrested in two other robberies.

Police say perpetrators in separate cases used similar robbery methods and appear to have shared information.