Embattled Senator Upakit Pachirirangkun has reported to drug suppression police, denied colluding in money laundering and a related criminal charge and was then released.
Kosolwat Inthajanyong, deputy spokesman for the attorney-general, told reporters the senator surrendered to the commander of the Narcotics Suppression Bureau's division 3 around 2pm on Monday.
Mr Upakit was jointly questioned by police investigators and public prosecutors in accordance with Section 134 of the Criminal Code.
The investigators charged him with being a senator colluding in money laundering and involvement in a transnational criminal organisation. He denied the charges, the spokesman said.
The senator was later fingerprinted for a criminal record examination. As he was not a person named in a summons or arrest warrant, he was released and requested to report again on April 17 for further questioning.
After being brought up to date, the attorney-general ordered police investigators and public prosecutors to accelerate and complete the investigation as soon as possible and to ensure fairness for all sides, Mr Kosolwat said.
Under Section 8 of the Prevention and Suppression of Involvement in a Transnational Criminal Organisation Act 2013, any person serving as a member of the House of Representatives, a senator, a local councillor, a civil servant, a state employee, a board member, an executive or manager of a state enterprise, or any person responsible for the operation of a financial institution, or any organisation under the constitution, who commits an offence under this section is liable for twice the normal penalty prescribed for the offence, a source explained.
Section 10 of the Anti-Money Laundering Act also provides for penalties up to three times the norm for an MP, senator or civil servant.
On March 17, Mr Upakit, 61, held a press conference to counter drug link allegations made by Move Forward Party MP Rangsiman Rome. The appointed senator denied any link with Myanmar national Tun Min Latt, who was arrested for drug trafficking last year.
He claimed Mr Rangsiman and some media outlets had made their own judgement that he was in the wrong. Mr Upakit also denied allegations that he had laundered money from the drug trade through an electricity supply business operating on the Thai-Myanmar border.
During the general debate in the House of Representatives last month, Mr Rangsiman blasted the government for its failure to tackle the problem of illegal drugs. Without giving names, the MP raised the allegations against a senator who was a long-time business partner of Tun Min Latt.
The Myanmar tycoon was arrested in Bangkok on Sept 17 last year. One of those arrested with him was the senator's son-in-law. Tun Min Latt has pleaded not guilty to drug trafficking charges. He remains in custody.