Chitra Ramkrishna, the former head of the country's largest stock exchange, was questioned for 12 hours by the CBI over the infamous 'tick by tick' market manipulation case.
An FIR, or first information report, was registered in the case earlier but new facts have come to light since, which is why Ms Ramkrishna was questioned, sources said.
The central agency has also posted notices against Ms Ramkrishna, former COO Anand Subramaniam, and her predecessor Ravi Narayan, to stop them from leaving the country.
Ms Ramkrishna, who was CEO and Managing Director of the National Stock Exchange from 2013 to 2016 before she quit for "personal reasons", is also under investigation for an alleged "glaring breach" of regulations - sharing confidential financial data with a 'yogi' living in the Himalayas.
The 'tick by tick' case was registered against OPG Securities; its Managing Director, Sanjay Gupta; Ajay Shah, who helped develop the software; and unknown officials from the NSE and regulatory body SEBI for alleged stock market manipulation from 2010 to 2014.
The case has to do with the alleged unfair dissemination of information from the market exchange's computer server to those of stock brokers. Both were set up in the same area - a scenario called co-location - offering the brokers a 10:1 (approximate) speed advantage over their competitors.
For the period of investigation (2010-2014), information was sent in a sequential manner from the stock exchange's servers to the brokers' through 'tick by tick'-based system architecture.
This meant the broker who connected first to the stock exchange's server received 'ticks', or the market feed, before the broker who connected later, giving him/her valuable information.
It is alleged that Sanjay Gupta had unfair access to this feed and this enabled his company, OPG Security Pvt Ltd, to access financial data a split second faster than his rivals.
And in the cutthroat world of stock markets, this is a massive advantage for any trader.
Yesterday, premises in Mumbai and other locations owned by Ms Ramkrishna and others were searched by the Income Tax Department in connection with the allegations she shared the bourse's financial projections, business plans and board agenda with a spiritual guru.
The guru was running the exchange and Ms Ramkrishna was "a puppet", SEBI has claimed.
Ms Ramkrishna has claimed the information- sharing did not compromise NSE operations.
The NSE, Ms Ramkrishna and senior official Anand Subramanian have been Rs 2 crore each, and the exchange has been barred from launching new products for at least six months.