Japanese police have seized more than 100 smartphones stolen in a series of robberies that took place in metropolitan Tokyo and beyond, investigative sources have said.

The police investigations are making progress gradually, with more than 50 people, including alleged perpetrators, having been arrested so far, as well as action taken against those who allegedly recruited the suspects.

But the alleged ringleaders have are yet to be identified, due in part to high levels of anonymity related to the cases. Police are rushing to analyze data contained in the seized smartphones, hoping for clues to the identities of those in charge.