The agency expanded its probe and grilled Ramkrishna, Narain and Subramanian in connection with the scam.
An audit report allegedly referred to Subramanian as a mysterious Yogi, but it was dismissed by the Securities and Exchange Board of India in its report on February 11.
The CBI has arrested former Group Operating Officer of NSE Anand Subramanian after expanding its three-year probe into the co-location scam.
He was questioned for days in Chennai before the agency decided to arrest him, the officials said.