Sources say officials of the Tokyo Olympics and Paralympics organizing committee and ad agency Dentsu, which were allegedly involved in bid-rigging, began making a list of companies to be assigned contracts in 2017, the year before bidding took place.

Tokyo prosecutors arrested Mori Yasuo, a former deputy director of the committee's operations bureau, Henmi Koji, a former senior Dentsu official, and two others earlier this month.

They are suspected of inappropriately steering contracts to specific companies and violating the anti-monopoly act. The contracts, which included work to develop plans for test events and the operation of main events, are believed to have been worth 40 billion yen, or about 300 million dollars, in total.

Mori and Henmi are suspected of preparing a list of companies that would receive contracts related to the planning of the Games' test events. They allegedly chose candidates based on their track records.

Sources say officials from the committee and Dentsu began to hold regular meetings on the matter in or around July 2017.

They say Mori's initial plan was to award discretionary contracts to companies without competitive bids. But in January 2018, committee officials effectively decided to conduct competitive bidding.

Despite that, it is suspected that committee and Dentsu officials continued to meet regularly to revise the list until April 2018, right before the start of the bidding processes.

Prosecutors believe the committee and the ad agency worked together to inappropriately manage the contract-awarding process, even after officials decided to hold the competitive bidding.