The Tokyo High Prosecutor's Office is set this week to begin questioning on a voluntary basis former executives of Japan Highway Public Corp. who went on to be hired by companies now embroiled in a massive bid-rigging scandal, sources said Saturday.

It would be the latest move in a scam involving rigging bids for steel bridge projects. Last week, prosecutors indicted 26 companies and eight senior employees for violating the Antimonopoly Law in connection with projects contracted by the government.

The prosecutors are now focusing their investigation on suspicions that similar bid-rigging took place for bridge projects ordered by Japan Highway, with the former executives serving as go-betweens.

According to the sources, prosecutors have questioned a 70-year-old former Japan Highway director who is currently an adviser to Yokogawa Bridge Corp. over allegations he played a leading role in organizing the bids for projects ordered by the public corporation.

They have also spoken to a 76-year-old man who was a former adviser to Mitsubishi Heavy Industries Ltd. after serving as vice president of Japan Highway, the sources said. This individual is suspected of handing over to the Yokogawa Bridge adviser the role of sorting out who won the bids.

Investigative sources said that the former director allegedly colluded with senior officials at Mitsubishi Heavy's bridge division to decide which firms would be the successful bidders for the Japan Highway projects.

The results of their discussions were reportedly relayed to the successful firm through 49-year-old Masami Seimiya, the former head of Ishikawajima-Harima Heavy Industries Co.'s bridge sales division, the sources said. Seimiya is among eight individuals who have been indicted in the scandal.