Now that the regulator is armed with two sets of tapes - one about Mr Rathi's call and the other a conversation between officials of the exchange - the next, and crucial stage of the probe is to establish a direct linkage between the call and trades put in by Mr Rathi or others.

Mr Rathi has also moved the court challenging a Sebi order restraining him from acting as a director on the BSE and also prohibiting him and his firms from carrying on business as a broker till further notice. Mr Rathi could not be reached for comment. ``We have only got some basic data so far. Now the job is to go through all the details of the trades and find out if a pattern exists,'' sources told The Financial Express. Already, there has been some reshuffling within Sebi on the Rathi tapes investigation, with Sebi's investigations chief LK Singhvi moving out of this part of the probe and executive director CM Mehra taking charge of it.

Investigative sources said Sebi would now go through all the details of the trades on March 2 not only on the BSE, but also on the NSE and also try and find out whether those who were present in Mr Rathi's room at the time were involved in putting through trades based on the call he made on that day.

In court, Mr Rathi's counsel had argued that as a president of the exchange, there was nothing wrong in his talking to the surveillance department. Mr Rathi, his counsel argued, was also a member of the surveillance committee of the exchange. In fact, the Rathi argument is that since on March 2 the market was already falling sharply and the executive director was not present at the exchange, it was necessary for him to enquire the cause of the hefty fall in the market. This was so since as the BSE president he would have to face questions not only from investors but also from the finance ministry.