A former Democrat spokesman wants to overturn the prosecution's decision not to challenge Panthongtae "Oak" Shinawatra's acquittal on money laundering charges last year.
The son of former prime minister Thaksin Shinawatra was acquitted by the Central Criminal Court for Corruption and Misconduct last November of conspiring and colluding to launder money.
Former Democratic Party deputy spokesman, Chao Meekuad, is now seeking to overturn the prosecution's decision not to pursue an appeal. He asked the DSI on Wednesday to seek ways to scrap the prosecution's decision.
The accusations were linked to a cheque worth 10 million baht that Mr Panthongtae received from a friend with close ties to the Krisda Mahanakorn Group. This group illegally obtained loans worth 9.9 billion baht from the state-run Krung Thai Bank (KTB) during the Thaksin administration.
The court ruled Mr Panthongtae not guilty of money laundering because prosecutors failed to prove he knew the source of the 10-million-baht cheque.
On May 26, the Office of the Attorney-General (OAG) decided not to appeal against the ruling, with Nate Naksuk, a deputy attorney-general, having signed off on the decision on behalf of the attorney-general.
This is the same Mr Nate who signed an order dropping all charges against Vorayuth "Boss" Yoovidhya in a hit-and-run case.
On Wednesday, Mr Chao said a court judge who worked on the case found Mr Panthongtae guilty and called for a four-year jail term. The DSI, which handled the case, also insisted on an appeal. However, the OAG did not proceed with the appeal.
Mr Chao said sceptics believe that Mr Nate's order was illegitimate. The law stipulates that only the attorney-general has the authority to make decisions regarding an appeal. No other person can act on the attorney-general's behalf or in the same capacity, he added.
The prosecution should have launched an appeal so the higher court could rule, he said.
Mr Chao said the DSI should petition the Central Criminal Court for Corruption and Misconduct or the Administrative Court to overturn Mr Nate's order.
Meanwhile, DSI deputy director-general Akkarapol Boonyopatsatam said the department will see if it had the legal power to take up Mr Chao's request.