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

The agency has also opened look out circulars against Ramkrishna, another former CEO Ravi Narain and former COO Anand Subramanian to prevent them from leaving the country.

The central probe agency had booked a owner and promoter of Delhi-based OPG Securities Pvt. Ltd, Sanjay Gupta and other 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 NSE, Mumbai and other unknown persons.

"It was alleged that the owner and promoter of 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 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.

Ramkrishna hit the headlines after a recent SEBI on February 11 said she was steered by a yogi, dwelling in the Himalayan ranges, in the appointment of Anand Subramanian as the exchange's group operating officer and advisor to the managing director (MD).

The SEBI charged Ramkrishna and others with alleged governance lapses in the appointment of Subramanian as the chief strategic advisor and his re-designation as group operating officer and advisor to MD.

Sebi levied a fine of Rs three crore on Ramkrishna, Rs two crore each on the NSE, Subramanian, former NSE MD and CEO Ravi Narain, and Rs 6 lakh on V R Narasimhan, who was the chief regulatory officer and compliance officer.

The Income Tax Department on Thursday had raided the premises of Ramkrishna and group operating officer, Subramanian, in Mumbai as part of a tax evasion investigation against them, official sources said.

The searches were aimed to check and gather evidence on the charges of financial irregularities and alleged tax evasion against the two, they said.

The premises of Ramkrishna and Subramanian were raided by officials of the Mumbai investigation wing of the Income Tax department early morning.

The Securities and Exchange Board of India charged Ramkrishna and others for alleged governance lapses in the appointment of Subramanian as the chief strategic advisor and his re-designation as group operating officer and adviser to MD.

The Sebi order added that Ramkrishna shared certain internal confidential information, including financial and business plans of NSE, dividend scenario and financial results, with the yogi and even consulted him over the performance appraisals of the exchange's employees.

Ramkrishna was the managing director (MD) and chief executive officer (CEO) of NSE from April, 2013 to December, 2016.

The regulator noted in its order that she refused to reveal the identity of the unknown person and sought to claim that the unknown person is a spiritual force.

Ramkrishna and Subramanian have been restrained from associating with any market infrastructure institution or any intermediary registered with Sebi for three years, while the same for Narain is two years.

Sebi also directed NSE to forfeit the excess leave encashment of Rs 1.54 crore and the deferred bonus of Rs 2.83 crore, of Ramkrishna.

In addition, Sebi barred NSE from launching any new product for six months.

Following these revelations, the Congress party had demanded that the government bring a white paper on the functioning of the NSE.

"The finance ministry and the prime minister should come out with a white paper on the state of affairs of National Stock Exchange and on the shocking activities of an 'invisible Baba' who was dictating terms to the former CEO of the exchange," Congress spokesperson Gourav Vallabh told reporters two days back.