The CBI has arrested former Group Operating Officer of National Stock Exchange Anand Subramanian after expanding its three-year probe into the co-location scam in the exchange in view of "fresh facts" emerging in a damning Sebi report, officials said on Friday.

Subramanian was taken into custody late Thursday night, they said.

He was questioned for days in Chennai before the agency decided to arrest him, the officials said.

The Securities and Exchange Board of India (Sebi) has charged former National Stock Exchange (NSE) CEO Chitra 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 has levied a fine of Rs 3 crore on Ramkrishna, Rs 2 crore each on 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.