Context: Government of Uttar Pradesh plans to perform polygraph and narcoanalysis tests as part of the investigation into the alleged gangrape and murder of a 19-year old Dalit woman by four men in Hathras.
What are polygraph and narcoanalysis tests?

• A polygraph test is based on the assumption that physiological responses that are triggered when a person is lying are different from what they would be otherwise.
• Instruments like cardio-cuffs or sensitive electrodes are attached to the person, and variables such as blood pressure, pulse, respiration, change in sweat gland activity, blood flow, etc., are measured as questions are put to them.
• A numerical value is assigned to each response to conclude whether the person is telling the truth, is deceiving, or is uncertain.

Background 

• A test such as this is said to have been first done in the 19th century by the Italian criminologist Cesare Lombroso, who used a machine to measure changes in the blood pressure of criminal suspects during interrogation. Similar devices were subsequently created by the American psychologist William Marstron in 1914, and by the California police officer John Larson in 1921.

Narcoanalysis, by contrast, involves the injection of a drug, sodium pentothal, which induces a hypnotic or sedated state in which the subject’s imagination is neutralised, and they are expected to divulge information that is true.

• The drug, referred to as “truth serum” in this context, was used in larger doses as anaesthesia during surgery, and is said to have been used during World War II for intelligence operations.
• More recently, investigating agencies have sought to employ these tests in investigation, and are sometimes seen as being a “softer alternative” to torture or “third degree” to extract the truth from suspects.
• However, neither method has been proven scientifically to have a 100% success rate, and remain contentious in the medical field as well.

Legality of the tests 

• In ‘Selvi & Ors vs State of Karnataka & Anr’ (2010), a Supreme Court Bench comprising Chief Justice of India K G Balakrishnan and Justices R V Raveendran and J M Panchal ruled that no lie detector tests should be administered “except on the basis of consent of the accused”.
• Those who volunteer must have access to a lawyer, and have the physical, emotional, and legal implications of the test explained to them by police and the lawyer, the Bench said.
• It said that the ‘Guidelines for the Administration of Polygraph Test on an Accused’ published by the National Human Rights Commission in 2000, must be strictly followed. The subject’s consent should be recorded before a judicial magistrate, the court said.

Legal status of its outcome

• The results of the tests cannot be considered to be “confessions”, because those in a drugged-induced state cannot exercise a choice in answering questions that are put to them.
• However, any information or material subsequently discovered with the help of such a voluntarily-taken test can be admitted as evidence, the court said.
• Thus, if an accused reveals the location of a murder weapon in the course of the test, and police later find the weapon at that location, the statement of the accused will not be evidence, but the weapon will be.