Legal and ethical dimensions of polygraph testing

Express Tribune

27-05-2025

The writer is a former Secretary to the Government, Home and Tribal Affairs Department, and a retired Inspector General of Police. He can be reached at [e-mail]
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The recent headlines regarding Imran Khan's refusal to undergo a polygraph test have reignited public discourse around the legal and ethical implications of such investigative techniques. The entry of digital tools like lie detectors into criminal investigations raises important questions: Can a suspect be compelled to undergo a polygraph test without their consent? Are the results of such tests admissible in a court of law?
To address these concerns, it is essential to understand what a polygraph test entails. Commonly known as a lie detector test, a polygraph measures physiological indicators — heart rate, blood pressure, respiratory rate and galvanic skin response — while the subject answers a series of questions.
The assumption is that deceptive responses produce physiological reactions distinct from those linked to truthful answers. However, polygraph testing is not based on an established scientific theory accepted in the field of law or physical science, and thus, its results are not considered conclusive evidence.
The legality of compelling an individual to undergo such a test touches directly upon constitutional protections, particularly the right against self-incrimination and the right to privacy.
In Pakistan, Article 13(b) of the Constitution provides protection against self-incrimination, stating: "No person accused of an offense shall be compelled to be a witness against himself." This constitutional safeguard underpins the principle of a fair trial, ensuring that individuals are not forced to provide evidence that may lead to their own conviction.
A landmark judgment in this context is the Indian Supreme Court's ruling in Selvi & Ors v. State of Karnataka (2010), which addressed the involuntary administration of narco-analysis, polygraph tests and brain-mapping techniques. The Court held that such practices violate Article 20(3) of the Indian Constitution, which guarantees the right against self-incrimination, and also infringe on Article 21, which protects personal liberty, including mental and physical privacy.
The Selvi judgment categorically stated that no individual can be compelled to undergo a polygraph test. Informed consent is mandatory, and even when consent is provided, procedural safeguards — such as legal representation and the presence of an independent medical practitioner — must be ensured.
Similarly, in the United States, forcing a suspect to take a polygraph test without their consent may violate the Fifth Amendment, which protects against self-incrimination.
The central legal question relates to the evidentiary value of polygraph results. Courts globally have expressed skepticism regarding the reliability and scientific validity of such tests.
In Selvi, the Indian Supreme Court clarified that while polygraph results may aid investigation if obtained with voluntary consent, they cannot form the sole basis for conviction. Such evidence, due to concerns over reliability and potential misuse, is inadmissible as substantive evidence.
In the United States, admissibility often hinges on the Frye and Daubert standards, which assess whether scientific evidence is generally accepted by the scientific community and meets established reliability criteria. Polygraph results frequently fail these tests, and thus, are typically excluded for fear they may unduly influence juries.
In the United Kingdom, polygraph tests are not used in criminal trials and have only limited application in investigative contexts. Across the European Union, the priority given to human rights leads courts to regard such techniques with caution.
In Pakistan, the Supreme Court's decision in Husnain Mustafa v. The State and another echoed this view. The Court recognised polygraph testing as a modern forensic tool capable of indicating deception but emphasised that its findings cannot be equated with an admission of guilt.
Beyond legal admissibility, polygraph testing raises significant ethical concerns. The possibility of coercion — whether overt or subtle — during the process of obtaining consent cannot be discounted. Moreover, physiological responses may be influenced by anxiety, medical conditions or the testing environment, rather than deception.
Another critical issue is the potential for institutional misuse. In high-profile cases, investigative agencies might use polygraph results to sway public opinion or create an illusion of progress, regardless of the scientific credibility of the findings. Over-reliance on such methods could divert attention from more reliable investigative tools like forensic analysis, corroborative witness testimony and digital evidence.
Polygraph tests also risk undermining the interrogative competence of law enforcement agencies. While these tests may offer psychological leverage or investigative leads, they must not be prioritised over constitutionally sound procedures or used at the expense of a suspect's fundamental rights.
There is broad consensus within the legal and academic community that individuals should not be compelled to participate in polygraph testing and that the admissibility of such results must be heavily restricted. Courts have rightly emphasised that criminal justice cannot be reduced to a spectacle reliant on questionable science.
The controversy surrounding Imran Khan's refusal to undergo a polygraph test underscores the delicate balance between science, law and ethics in criminal jurisprudence.
While polygraph tests may have a supplementary role in investigations, their inherent limitations must not be overlooked. Legal frameworks must continue to uphold voluntariness, due process and the right against self-incrimination — ensuring that justice is not only done but is seen to be done in a fair and constitutionally sound manner.