Polygraph Testing: A Double-Edged Sword in Modern Legal Investigations

The polygraph, referred to as the “lie detector,” has historically been a subject of significant scholarly interest and controversy within the domains of law enforcement, security, and forensic investigation. Advocates of this technology contend that it serves as an essential instrument for revealing deception, as it purportedly identifies physiological variations linked to lying, including modifications in heart rate, blood pressure, respiration, and skin conductivity.

The inception of the polygraph can be traced to the early 20th century. Researchers William Marston and John Augustus Larson initiated experimental endeavours employing diverse methodologies to quantify physiological reactions in a quest to ascertain falsehoods. With time, the polygraph has experienced significant evolution, characterised by enhancements in sensor technologies and data analytical methodologies that facilitate more precise and dependable assessments of the physiological alterations potentially linked to deceptive behaviour.

In India, several high-profile cases have involved the use of polygraph tests. Notable cases from the 1990s include the Bombay Bomb Blast Case (1993), where Yakub Menon was convicted for his role in the serial bombings, and the Shivani Bhatnagar Journalist Murder Case (1999). In the 2000s, the Nithari Hatya Kand (2005), while the Aarushi Talwar Murder Case (2008) captured public attention. In 2007, the Mecca Masjid Hyderabad Case and the Madhumita Shukla Murder Case were widely covered. In the 2010s, cases like the Adarsh scam (2011), the Sheena Bora Murder case (2012), the 2G scam case (2012), and the Vyapam case (2013) highlighted the role of polygraph testing in complex fraud and murder cases. In 2015, the Udahmpur Attack Case, involving a Lashkar-e-Taiba terrorist, and the Pathankot Airbase Attack case (2016) also saw using polygraph tests for interrogation. Hathras gang rape case (2020), Shraddha Walker Murder case (2022), and Kolkata rape-murder case (2024), are some of the recent major cases where polygraph has been used.

The Supreme Court has adopted a sophisticated perspective regarding the utilisation of polygraph results as evidentiary material in judicial processes. The Supreme Court has acknowledged the utility of polygraph examinations as a method for collecting evidence, particularly in scenarios where alternative forms of evidence may be deficient. The court has concurrently articulated apprehensions concerning their dependability and admissibility as legal evidence. In the seminal case of Selvi & Ors. vs. State of Karnataka (2010), the Supreme Court decreed that no person may be compelled to undergo a polygraph examination without their explicit consent, underscoring that such procedures are intrusive and infringe upon the fundamental right against self-incrimination as enshrined in Article 20(3) of the Indian Constitution. However, the court has allowed voluntary polygraph tests, but any information obtained may be used as supplementary or corroborative evidence.

Recent scientific innovations have sought to improve the precision of polygraph tests by exploring alternative methodologies, including the use of artificial intelligence algorithms and machine learning techniques. These approaches aim to analyse polygraph data with greater accuracy, reducing the occurrence of false positives and enhancing overall reliability. These algorithms are designed to identify subtle physiological patterns that may elude detection through traditional polygraph methodologies. As scientific and technological paradigms progress, the polygraph may ultimately establish itself as a more dependable and ethically justified instrument for truth verification; nonetheless, it is imperative to uphold a prudent and deliberate approach to its application within the judicial system.

(Keshav Kumar is a retired IPS and forensic consultant to Assam Government. Samiksha Das is Forensic Psychologist, Assistant Lecturer (OPJGU). Views personal.)