The CBI 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 lookout 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.