RG Kar rape case accused, six others undergoing ‘lie detector’ test, but is it admissible in court?

Polygraph tests, commonly called “lie detection” tests, began Saturday for 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 in West Bengal.

The polygraph test on the main suspect, Sanjay Roy, is being conducted at the prison where he is currently held. The remaining six individuals, including former principal Sandip Ghosh, four doctors who were on duty the night of the incident, and a civil volunteer, will undergo the test at the Central Bureau of Investigation (CBI) office.

A team of polygraph specialists from the Central Forensic Science Laboratory (CFSL) in Delhi has travelled to Kolkata to carry out these tests, officials said.

Are polygraph tests accurate?

Polygraph tests, widely used in law enforcement and national security, are designed to detect deception based on physiological responses such as heart rate, blood pressure, respiration, and skin conductivity.

However, their accuracy remains controversial, as these physiological changes can be triggered by factors like nervousness, fear, or anxiety, rather than lying. A 2004 study by the American Psychological Association stated that there is no scientific evidence to support a unique physiological reaction associated with deception.

Countermeasures, including physical movements, psychological tactics, and pharmacological agents that alter arousal patterns, may also undermine the accuracy of polygraph tests.

However, the American Polygraph Association cites data indicating that single-issue diagnostic polygraph tests have an aggregated decision accuracy of 89 per cent, with an 11 per cent rate of inconclusive results. Tests involving multiple issues have an aggregated accuracy of 85 per cent, with a 13 per cent inconclusive rate.

Are polygraph tests admissible in court?

In India, polygraph test results cannot be considered “confessions”. However, any evidence or material discovered as a result of such a voluntarily administered test can be admissible in court. For example, if an accused person, during the test, reveals the name of a witness they threatened, or where the hidden footage is kept, and the witness subsequently testifies, the witness’s testimony may be admitted, although the accused person’s statement itself would not be.

The law varies from country to country. Polygraph test results are admissible in courts in Belgium, Colombia, and Poland. In China, they are admissible in civil cases, but not criminal ones.