The CBI on Friday questioned Chitra Ramkrishna, the former CEO of National Stock Exchange, after fresh facts emerged in connection with its ongoing probe into the 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 the owner and promoter of Delhi-based OPG Securities, Sanjay Gupta, and others in connection with the 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 the Securities and Exchange Board of India (Sebi) and National Stock Exchange (NSE), Mumbai and other unidentified persons.

“It was alleged that the owner and promoter of the said private company abused the server architecture of NSE in conspiracy with unknown officials of NSE. ”

“It was also alleged that unknown officials of NSE, Mumbai had provided unfair access to the said company using the co-location facility during the period 2010-2012 that enabled it to login first to the exchange server of the stock exchange that helped to get the data before any other broker in the market,” the CBI has alleged in the FIR.

In the high-frequency algorithmic trading on the NSE, an edge of a few seconds to a stock broker in a trade can make a huge difference, the officials said.

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.

Gupta once again managed the data centre staff of the NSE to get connected to the backup servers which were with zero load and provided far better and faster access of market feed to OPG Securities in comparison to other brokers, the CBI has alleged.