The CBI on Thursday submitted a prayer in the Sealdah court to carry out a polygraph — or lie-detection — test on six persons, including Sandip Ghosh, who resigned as principal of RG Kar Medical College and Hospital after the rape and murder.

Among the others on whom the agency wants to conduct the test are four junior doctors who were on night shift with the postgraduate trainee who was raped and murdered.

The sixth person who the agency wants to undergo the test is Sourav Bhattacharya, a Kolkata Police civic volunteer who allegedly accompanied prime accused Sanjay Roy to several places on the night of the crime.

The prayer was accepted and the six were taken to the court where their consent was sought for the test. No one can be subjected to a polygraph test without his or her consent.

Sources said all six had given their consent.

During the polygraph test, the person is asked a few questions to which he or she has to answer in “yes or no”.

“It is a lie-detection test during which a person is asked a few questions and his or her body parameters such as heart rate, blood pressure and minute body responses are monitored. Usually, a wrong answer can be detected through fluctuations in the parameters,” said a forensic doctor not involved in the investigation in the RG Kar case.

The CBI till Thursday questioned Ghosh and the other five several times. “But we would like confirmation through the polygraph test,” said an officer in the central agency.

Failing a polygraph test does not make the person susceptible to arrest or legal action. But law enforcement agencies often use the test to know whether the investigation is proceeding in the right direction.

Ghosh was questioned by the CBI for the seventh consecutive day on Thursday. He was taken to the agency’s office in the CGO Complex in Salt Lake after he gave his consent for the polygraph test.

CBI sources said the four doctors who were on duty with the woman on August 8 night (the postgraduate trainee’s body was found the next morning) have been questioned several times — both by Kolkata Police and the CBI.

“All of them have claimed that they left the seminar hall (where the body was found) at some point and attended to patients in the Emergency Building. We have collec-
ted details of head tickets of the patients whom these doctors have claimed to have treated that night,” said an officer.

Civic volunteer Sourav Bhattacharya was found to have spent a considerable time with accused Sanjay Roy on August 8 night, sources in the agency said.

“He and Roy had gone to several places that night before coming back to RG Kar Medical College and Hospital on August 9 morning. Bhattacharya has claimed to have parted ways with Roy while they were entering the hospital. He said he was not involved in the crime,” a CBI officer said.

The central agency has also submitted a prayer in the court for permission to record statements of the four junior doctors.