Tokyo police are expected to establish a mass fraud case against the head of a Tokyo-based investment group for allegedly swindling money from tens of thousands of people, according to police sources.

The Metropolitan Police Department will likely arrest the leader of the G.O. group, Genta Ogami, 39, and the group's senior members as early as this month, they said.

The group, established by Ogami in 1996, is suspected of swindling most of the 40 billion yen they had collected as investments from more than 30,000 people across Japan, the sources said.