“It’s clear that some people in the market knew about the deal. They might have bought the shares anticipating a rise when the deal is made public later. It’s not clear whether this is insider trading. There could be leak of information from somewhere,” said BSE dealer Pawan Dharnidharka. As per the Sebi rules, investors should not trade in shares using price-sensitive information — that is, information known only to a select group of people.

According to market circles, there was a big rise in volumes to 38.31 lakh shares on the BSE on June 10 (Tuesday) — one day before the deal was made public — from just 9.29 lakh on June 9. The stock shot up by 5 per cent before closing flat on Wedesday. “The stock tested an intra-day high of Rs 591.8 on the NSE, but closed at Rs 561 with sell order of 27,101 shares at the post-closing session,” said an analyst with Geojit Financial Services.

Asked to comment on the movement, a Ranbaxy official said there was nothing unusual about the scrip’s movement. “The scrip has been moving upwards in the last two or three months. In fact, the entire pharma sector has been undergoing a re-rating,” the offficial explained.

When contacted, a Sebi official did not comment on the scrip movement. However, market circles say that it’s common to see share prices of companies show unusual movement ahead of any major announcement like takeover or merger. Though Sebi has put in place rules to prevent insider trading, they were found ineffective. The regulator is now in the process of finetuning the takeover guidelines.