As the prime accused in Kolkata rape-murder gears up for a polygraph test, how reliable are these lie detectors?

The controversy surrounding the reliability of lie detectors has persisted for decades. A local Kolkata court recently approved the administration of a polygraph test on Sanjoy Roy, the prime accused in the recent rape-muder case that has shaken the country. This decision has reignited debates over whether lie detectors genuinely serve justice or merely offer a veneer of truth-finding.

Reliability of lie detectors

Lie detectors, more formally known as polygraphs, measure physiological responses such as heart rate, blood pressure, respiration, and skin conductivity. The underlying assumption is that when a person lies, they experience stress or anxiety, leading to measurable changes in these physiological markers. A trained examiner interprets these responses to determine whether the person is lying or telling the truth.

Despite their use in criminal investigations and courtrooms, the reliability of lie detectors remains highly contested. Critics argue that polygraphs are not scientifically robust enough to be considered reliable. The primary concern is that physiological responses can be triggered by a variety of factors unrelated to lying, such as nervousness, fear, or even anger. This makes it difficult to definitively link changes in physiological responses to deception.
Studies have shown that polygraphs are far from foolproof. While research has varied, the National Research Council published a report in 2003 questioning the efficacy of polygraphs, stating that the evidence that they are accurate is "scientifically weak" and that their results should be treated with caution. Moreover, the American Psychological Association has also expressed scepticism, noting that "most psychologists agree that there is little evidence that polygraph tests can accurately detect lies."

Major cases where lie detectors were used

Despite these concerns, lie detectors have played significant roles in various cases in India. This includes one of the most horrific serial murder cases in India, the Nithari killings in 2007 which involved the discovery of numerous bodies and human remains near the house of businessman Moninder Singh Pandher in Noida. Pandher's domestic help, Surinder Koli, was accused of carrying out these brutal murders. During the investigation, both Pandher and Koli were subjected to polygraph tests. While Koli eventually confessed to the murders, the polygraph tests were part of the investigative process that led to his conviction.

In more recent years, polygraphs have been used in cases such as the O.J. Simpson trial, where Simpson had refused to take a polygraph test. However, O.J. Simpson reportedly did take the test shortly after, with results of this test indicating that he was being deceptive towards the questions he answered.
However, polygraphs have also been involved in miscarriages of justice. For example, in the case of William Dillon, who was wrongfully convicted of murder in 1981 based partly on a failed polygraph test, it took nearly 27 years before DNA evidence proved his innocence. Such cases underscore the potential dangers of relying too heavily on lie detectors in legal proceedings.

Where are lie detectors still used?

The use of polygraphs varies widely across the world. In India, polygraph tests are not admissible as evidence in court unless the accused consents to the test. The Supreme Court has also ruled that polygraph tests can be considered material evidence, but they may not be enough to convict someone. However, they are still occasionally used in investigations, as seen in the Kolkata case.

Some researchers are exploring more advanced techniques, such as brain imaging and voice stress analysis, to detect lies. However, these methods are still in their infancy and come with their own set of ethical concerns.

In conclusion, while lie detectors may offer some utility in investigations, their reliability remains highly questionable. The decision to use them, particularly in high-stakes cases like the one in Kolkata, should be approached with caution.