Kolkata/IBNS: Failing to get satisfactory answers, the Central Bureau of Investigation (CBI will now conduct a polygraph test on RG Kar Hospital's former Principal Sandip Ghosh and four other doctors, who were on duty the night of the brutal rape and murder of the 31-year-old trainee doctor at the premises.

The central agency has received a nod from a special court for the test.

The results of a polygraph test, while not admissible in court, are often said to point investigators in the correct direction. 

The CBI has been grilling Sandip Ghosh every day for the last week. However, officials say they are yet to get a satisfactory response.

Sandip Ghosh is under scanner for the misinformation given to the deceased doctor's parents and the delay in filing a complaint with the police.

Both the Supreme Court and the Calcutta High Court have repeatedly focussed on his role, raising multiple questions.

Earlier in the day, the top court asked questions about why the case was tagged an unnatural death.

A case of unnatural death is usually filed when there is no formal complaint. The court had said it is the duty of the head of the institution in such cases to lodge a formal complaint.

"Why did the Principal not come to file the FIR? Was anyone stopping him? Why was he transferred to another hospital? The court wants to know the reason for all this," Chief Justice of India DY Chandrachud asked.

The Kolkata Police have registered a corruption case against the former Principal.

An investigation is in progress into the financial irregularities at the state-run RG Kar Medical College, a complaint which was filed in June.