The CBI on Friday questioned former CEO of National Stock Exchange Chitra Ramkrishna in the view of fresh facts emerging in connection with its ongoing probe into alleged abuse of co-location facility in the NSE, officials said.

The CBI has also issued look out circulars against Ramkrishna, another former CEO Ravi Narain and former group operating officer Anand Subramanian to prevent them from leaving the country.

The central probe agency had booked owner and promoter of Delhi-based OPG Securities Sanjay Gupta and others in connection with alleged abuse of NSE co-location facility to make gains by getting early access to the stock market, they said.

The agency was also probing unidentified officials of Securities and Exchange Board of India (SEBI) and National Stock Exchange (NSE), Mumbai and other unidentified persons.

It has emerged that Gupta was the first to log in in 90 per cent of cases which prompted murmurs in the stock broker circuit, and resulted in a load balancer being introduced by the NSE, the officials said.