Kolkata, Sep 13 (IANS): After polygraph test, CBI has sought permission from a special court in Kolkata to conduct a narco-analysis of Sanjay Roy, the accused in the rape and murder of a junior doctor at RG Kar Medical College & Hospital here last month.

According to sources, CBI now wants to match the report of the polygraph test with that of the narco-analysis, provided they get the permission of the court for this.

There is a basic difference between polygraph test and narco-analysis: polygraph, test also popularly known as "lie detector" test measures physiological responses like blood pressure, pulse, and respiration of the person who is being questioned based on the idea that physiological responses of a person are different when they are lying.

On the other hand, narco-analysis involves injecting the person to be questioned with sodium pentothal, popularly termed “truth drug” or “truth serum,” which puts the person concerned in a stage of hypnosis which is believed to make that person speak only the truth.

None of the tests can be conducted without the consent of the person on whom they are conducted.

On Wednesday evening, CBI officials had collected the teeth impression of Roy. Sources said that the teeth impression of the accused is often considered important evidence in case of any investigation in rape or rape and murder cases; and since Roy is the sole arrested accused in the case so far, the needful has been done.

Roy was initially arrested by the cops of the special investigation team of Kolkata Police, who were carrying out the initial investigation in the matter before a division bench of Calcutta High Court handed over the charge of the probe to CBI.

Right now, the main focus of the investigation of CBI is to be sure whether Roy was the only perpetrator of the crime or whether there is involvement of others in the matter, the investigating officials are also looking at suspected tampering of evidence as well as severe lapses on the part of the city police which conducted the initial probe before it was handed over to them.