The lie detection tests on the main accused and six others in the alleged rape and murder of a trainee doctor at Calcutta’s RG Kar Medical College and Hospital began on Saturday, officials said.

The polygraph test on Sanjay Roy, the main accused, is being conducted in the prison where he is lodged, while the remaining six, including former principal Sandip Ghosh and four doctors who were on duty during the night of the incident and a civic volunteer, are undergoing the test at the agency's office in Calcutta, they said.

Ghosh arrived at the CBI's office at CGO Complex in Salt Lake on Saturday morning for the ninth day consecutive day, and was then taken for the test, the officials said.

Those undergoing the lie detection test include two first-year postgraduate trainees, as investigators allegedly found their fingerprints inside a seminar hall at the state-run medical facility where the medic's body was discovered, an official said.

A team of polygraph specialists from the Central Forensic Science Laboratory (CFSL) in Delhi have flown to Calcutta to conduct these tests, he said.

The CBI told the Supreme Court on Thursday that there was an attempt to cover up the alleged rape and killing of the post-graduate doctor by the local police, as the crime scene was altered by the time the federal agency took over the probe.

The trainee doctor’s body with severe injury marks was found inside a seminar hall of the hospital's chest department on the morning of August 9. Roy was arrested the following day.

On August 13, the Calcutta High Court ordered the transfer of the probe from the Kolkata Police to the CBI, which started its investigation on August 14.

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