After arresting Chitra Ramkrishna and Anand Subramanian, CBI will now focus on the roles of other NSE officials and brokers.According to CBI sources, the investigation so far has revealed that NSE and SEBI officials were bribed by the accused firm OPG securities — a possible reason they turned a blind eye to the irregularities in the co-location facility.Once Chitra was appointed as the MD, CEO in 2013, the NSE stopped issuing warnings to OPG securities to stop violating co-location facility guidelines of NSE.Also Read: Yogi's identity, magnitude of scam and how Ramkrishna knew Subramanian in CBI's line of questioningCBI sources told CNBC-TV18 that the role of CTO, NSE Muralidharan Natarajan is also under CBI scanner. Natarajan was responsible for putting in place the architecture of the co-location facility and was reporting to Chitra.Chitra has already blamed her subordinates for the irregularities in the co-location facility. So, to find out if Muralidharan had any involvement in the scam will be an important aspect of Chitra's interrogation.Also Read: EXCLUSIVE | NSE co-location scam: CBI arrests former NSE CEO Chitra RamkrishnaCBI will interrogate Chitra to find out about the involvement of other NSE officials and brokers. CBI will also confront Chitra with the digital evidence collected so far.Chitra Ramkrishna, former MD-CEO of NSE was arrested by CBI on March 6. Before this, Anand Subramaniam, former GOO of NSE was arrested by CBI on the intervening night of February 24-25.Chitra and Subramanian are accused of conspiring with brokers and abusing NSE co-location facility.