The National Anti-Corruption Commission (NACC) plans to seek assistance from the Chinese embassy to examine Chinese companies implicated in the controversial sale of rice paddy under the government-to-government deal.
NACC secretary-general Sansern Poljiak announced the move after the anti-graft agency agreed to press charges against 91 firms, two of which are registered in China.
The companies will be charged with supporting the offences, and the NACC is now in the process of summoning executives or managers from these firms, he said.
Since more than 90 private firms are implicated in the case, the inquiry will not be over anytime soon. It remains unclear when the probe will be completed, Mr Sansern said.
"From the information [on the companies involved] I have seen, I think investigations in this case should take a very long time," the NACC secretary-general said.
The NACC had earlier pressed malfeasance charges in connection with the case against former commerce minister Boonsong Teriyapirom, former deputy commerce minister Poom Sarapol and former director-general of the External Trade Department Manas Sroypol.
Three people — Rathanit Sojirakul, Somkid Ueansupha and Litr Phoja — allegedly connected with a rice export firm which played a key role in selling the paddy are facing legal action.
Some have appeared at the NACC to defend themselves, Mr Sansern said.
"Mr Boonsong has testified and asked the NACC to conduct further probes into the case," said Mr Sansern, adding that the anti-graft agency is looking at the finer details of the investigation.
The NACC has found no evidence that two implicated firms — Guangdong Stationery & Sporting Goods Import & Export Corp and Hainan Grain & Oil Industrial Trading Co — were authorised by the Chinese government to purchase paddy under the rice-pledging scheme.
It also found no evidence that the rice had been exported to China.
The rice-pledging scheme is a key Pheu Thai policy, but has drawn harsh criticism from many quarters over graft and for swelling public debt.