The CBI has sought permission from a Kolkata court to conduct a polygraph test on city police assistant sub-inspector Anup Dutta who was said to be close to Sanjay Roy, the arrested accused in the rape and murder of a trainee doctor at RG Kar medical college, officials said Tuesday.

The CBI is exploring if Dutta helped Roy in any cover up of the crime, they said.

According to reports, Dutta was allegedly instrumental in extending various favours to Roy, they said.

The central probe agency is trying to find out if Roy told Dutta about the crime and received any help, they said.

They said the court would decide the application for a polygraph test after seeking Dutta's consent on the issue.

The CBI completed polygraph tests on former principal of the medical college Sandip Ghosh on Tuesday, the third day of subjecting him to a series of Deception Detection Tests (DDT), they said.

He underwent a Layered Voice Analysis test on Saturday, followed by a polygraph test on Monday. The test on Monday could not be completed, so it was resumed on Tuesday.

Layered voice analysis is a new DDT in the forensic experts' arsenal. It detects the speaker's reaction to a lie but does not identify a lie. The technology identified stress, cognitive processes, and emotional cues in different voice properties.

A polygraph test, also a DDT, can help assess inaccuracies in statements of suspects and witnesses. By monitoring their psychological responses -- heart rate, breathing patterns, sweating, and blood pressure -- investigators can determine if there are discrepancies in their responses.

However, these are not admissible evidence during the trial and can only be used to get further leads in a case.