Yingluck sold 278,400 AIS shares in a price range of Bt101-113 during the period, when rumours about the takeover of AIS’s parent company were intensifying, raising several ethical and legal questions concerning the practice as well the stock exchange itself.

Some other AIS executives were also unloading their shares in large numbers during the same period.

Responding to a question concerning the conduct of the AIS executives and the rules on insider trading, Kittiratt was quoted by Prachachat Turakij as saying: “We are looking into it at the moment. But let me ask where have you been for the six months before that? Do you know how many times they informed the authorities and how many times they sold? To assume that someone has done something wrong, you have to look far beyond one short period. They had been selling their shares all the time and reporting the sales as usual. I’d like to see our news media do better homework.”

When asked if his reply meant that he saw nothing wrong with the share sales by AIS executives, he said: “I’m just pointing out what we should also look at. Don’t ask for our opinions yet, because we haven’t finished our homework [investigation] yet.”

That “homework” will have to finish soon, with social pressure mounting for the stock exchange to clear itself of charges that it turned a blind eye to questionable transactions during the complicated process of Shin Corp’s takeover by Singapore’s Temasek Holdings.

The Securities and Exchange Commission has also insisted that the ball is in Kittiratt’s court before it can launch a formal, all-out investigation.

“All information is with the stock exchange, which is required to make the preliminary inquiry since it has all the information,” a senior SEC official said.

The SET is already under the spotlight following discovery that a major transaction in Shin Corp shares on January 20 did not appear on the exchange’s main trading board on the day it took place.

The secrecy surrounding the sale of the 329,200,000 Shin shares by Ample Rich Investments, an obscure company registered in the British Virgin Islands, to Prime Minister Thaksin Shinawatra’s son and daughter has raised questions about how the exchange could have missed such a big-lot transaction and whether there was an effort to keep this significant transaction from public knowledge.

The stock exchange as well as the SEC also face the potentially explosive question of when exactly they became aware of the takeover. Shin Corp shares had been allowed to be freely traded despite strong rumours and conspicuous sales and transactions involving executives and major shareholders.

If there is proof they had knowledge of the impending takeover beforehand, the next question will be whether they acted to fulfil their duty of protecting the country’s and small investors’ best interests.