The CBI on Saturday spared Sandip Ghosh, former principal of RG Kar Medical College and Hospital, further questioning and remained busy compiling data they have collected so far while probing the rape and murder of the postgraduate trainee of the hospital.

Ghosh has so far been questioned by the CBI on over 15 occasions for long hours.

Senior CBI officers said they were trying to match statements of those from the chest medicine department who first spotted the junior doctor dead in the seminar room at RG Kar with those of the Kolkata Police officers who reached the crime scene after receiving the information.

Details of the two accounts from the two sets of people — the police and doctors — are crucial in figuring out whether there was any deliberate loss of valuable time after the murder was detected, the officers said.

The hospital authorities told the police they came to know about the death of the postgraduate trainee at 9.45am on August 9. Senior investigating officers of the Kolkata Police said they received the first intimation at 10.10am.

Besides trying to join the dots, officers of the central agency said they were trying to collect more information about some of those with whom the deceased junior doctor would converse frequently on her mobile phone.

An initial list of such names has been drawn up, but the officers said they were planning to question a few others who would often speak to the victim.

The process of selecting the names based on call details records is time-consuming, they said.

The officers said they want to talk to some of the colleagues of the deceased doctor again to ascertain some of the information that has reached the agency so far.

The CBI has so far questioned more than two dozen witnesses and conducted polygraph tests on around 10 people in connection with the court-monitored investigation into the case of rape and murder of the 31-year-old junior doctor of RG Kar Medical College and Hospital.

The central agency, however, has not been able to arrest anyone.

Officers said they were not going by popular opinion but by pieces of evidence that they have collected so far in the course of the probe.