Former Democrat MP Watchara Phetthong on Monday petitioned the National Anti-Corruption Commission (NACC) to investigate Office of the Attorney General (AOG) officials accused of malfeasance over a decision not to appeal against the acquittal of Panthongtae "Oak" Shinawatra.
The Central Criminal Court for Corruption and Misconduct cleared Mr Panthongtae of charges of conspiring and colluding to launder money on Nov 25 last year.
The OAG on May 26 decided not to appeal against the ruling, with a deputy attorney-general having signed off the decision on behalf of the attorney-general.
Mr Watchara said the attorney-general, deputy attorney-general and prosecutors neglected their duties and violated Section 157 of the Criminal Code when they decided against pursuing a conviction at a higher court.
The accusations against Mr Panthongtae were linked to a 10-million-baht cheque he received from a friend with close ties to the Krisda Mahanakorn Group, which had been plagued by non-performing loan issues.
Yet, the group illegally obtained loans worth 9.9 billion baht from the state-run Krung Thai Bank (KTB) during the Thaksin administration.
Mr Watchara said the decision was unjust because a court judge found Mr Panthongtae guilty and called for a four-year jail term and the Department of Special Investigation, which handled the case, also insisted on an appeal.
He said the prosecution's move conflicted with its decision to indict Mr Panthongtae, noting it was strange for public prosecutors to stop pursuing a conviction at the first court.
The ex-Democrat MP submitted some cases showing the prosecution deciding to pursue convictions with higher courts even though doing so was not deemed to be of public interest.