TOKYO -- Investigators looking into bid-rigging on projects related to Japan's next-generation bullet train line have questioned former executives of contractors Taisei and Shimizu, sources close to the probe said on Wednesday. 

Obayashi, another contractor, has been a focus of the investigation, due to suspicions that it cheated to win the contract for an emergency exit on the planned maglev line, the Linear Chuo Shinkansen. Executives of Kajima -- Obayashi's sole rival in the last round of bidding for the project -- have also been questioned. But the authorities' move to interview former officials of other companies suggests there may have been foul play in earlier bidding processes.

The sources also revealed that Obayashi's final bid for the emergency exit was about 10% lower than Kajima's. Both contractors were bidding through joint ventures they led.

Special investigators with the Tokyo District Public Prosecutors Office suspect an insider at JR Tokai, the railway company that held the bidding, may have told Obayashi about the available budget and rivals' terms. This may have enabled Obayashi to go comfortably lower than its competitor in the final round. 

The exit is to be built in Nagoya, leading from the track tunnel up above ground. JR Tokai began soliciting bids in 2015.

The first round ranked bidders based on everything from prices quoted and technological capabilities to their project track records. In the second round, JR Tokai negotiated prices with the top contenders. In the end, a joint venture formed by Obayashi, Toda and JR Tokai Construction won the deal at about 9 billion yen ($79.5 million).

The Kajima joint venture quoted a total price of about 10 billion yen and lost, the sources said.

Obayashi is also suspected of seeking rivals' cooperation to allow it to prevail.

(Nikkei)