New Delhi | The lie detection tests on the main accused and six others in the alleged rape and murder of a trainee doctor at the state-run RG Kar Medical College and Hospital started on Saturday, officials said.

The polygraph test on the main accused, Sanjay Roy, will be 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 civil volunteer, will undergo test at the agency's office, the officials said.

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

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

The rape and killing of the junior doctor in a seminar hall of the hospital has sparked widespread protests.

The medic's body with severe injury marks was found inside the seminar hall of the hospital's chest department in 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.