"The SEC spent a year collecting information and evidence. As the SEC was about to launch an in-depth investigation, Department of Special Investigation (DSI) director-general Sunai Manomai-udom told us to forward what we had to the DSI without filing charges, because they had a team and more expertise for such in-depth investigations," Thirachai said in an interview with Krungthep Turakij.

He noted that SEC officials also joined the DSI investigation team and that the investigation progressed quickly under the DSI. Within three months, the investigation was concluded.

"This progress was partially attributable to the SEC's preparation of information and does not mean the SEC delayed the investigation. We had comprehensive cooperation with DSI," Thirachai.

His interview followed criticism of the SEC for slow action against alleged malfeasance of politically influential figures concerning listed companies. Though hailed for its actions against Picnic's shareholders, it was heavily criticised for slow action in the Shin Corp case. The SEC earlier decided not to bring insider-trading charges against Advanced Info Service executives who sold shares ahead of the announcement of the Shin acquisition deal. Even though it fined Thaksin's son, Panthongtae, for failing to include Shin shares held by Ample Rich Investments in his filings, the fine was generally considered too small.

That it did not charge Thaksin with violating the securities law and let the DSI file charges also sparked questions about the SEC's integrity and flaws in its operations.

This is in stark contrast to the SEC under the reign of former secretary-general Ekamol Khiriwat, when big-time investors were charged en masse with insider trading.

Thirachai explained that in the past, the SEC conducted its own investigation and filed charges against wrongdoers. Then the cases would be passed on to the DSI. However, he said it was harder for the SEC to find evidence single-handedly without the DSI's cooperation. As such, the process is adjusted to fit changing circumstances and evidence. The SEC only files charges when it has clear evidence, such as in insider-trading cases, but seeks cooperation from the DSI in more complicated cases.

"In the past, we've seen attorneys refuse to prosecute some cases, and the SEC has also faced counter-suits. This adjustment to the legal process is meant for fairness for all and accessibility to information in complicated cases," Thirachai said.

He insisted the SEC was free from the intervention of business-led political groups and that there was a structure to ensure fair treatment under a single set of standards.

He also said he was ready to answer any questions about SEC operations that will reportedly be asked by the Assets Examination Committee (AEC).

"We have not received any questions from the AEC, and so far, as SEC secretary-general, I have testified to the AEC in many cases and submitted all information as requested. I must insist here that the SEC's operations are transparent and independent. I'm willing to explain all aspects of the operations to the AEC if it has any questions," he said.