Former permanent secretary for finance and the ex-director general of the Revenue Department are among 45 Finance Ministry officials under investigation for failing to demand Thaksin Shinawatra pay 17.6 billion baht in tax on profit made from the sale of shares in Shin Corp in 2006.
The case concerns former premier Thaksin's children, Mr Panthongtae and Ms Pinthongta, who purchased 329 million Shin Corp shares at a price of one baht each from Ample Rich, an offshore holding company controlled by the Shinawatra family.
The pair later sold the shares in their names to Singapore's state-owned company Temasek Holdings through the Stock Exchange of Thailand for 49.25 baht each, reaping capital gains of nearly 16 billion baht.
The case went to the Central Tax Court which in 2010 ruled in the siblings' favour. According to the court, the real owner of the shares was Mr Thaksin, not his two children.
It is alleged that after the ruling the ministry officials did not make an effort to demand the tax from Thaksin and did not appeal the case to the Supreme Administrative Court.
Inspector-general Yuttana Yimgarund, who is chairing a Finance Ministry panel into the matter, said the body is zeroing on 45 ministry officials to discover why they failed to tax the former prime minister.
The officials who are under investigation include the then permanent secretary of finance, the director-general of the Revenue Department, deputy director-generals, the directors of bureaus and chiefs of subdivisions, according to Mr Yuttana.
The probe is due to be wrapped up by next month, he noted.
The panel questioned four officials from Regional Revenue Office 3 who were in charge of collecting the tax on the Shin Corp share sale, claiming there are grounds to proceed with disciplinary action against them, said a ministry source. The officials have denied they had the authority to tax the sale.
In July last year, the Criminal Court sentenced four former government officials to three years in prison for helping Mr Thaksin's children evade the 16 billion baht in taxes.