The prosecution may now have to work that much harder. In many cases, the prosecution may now never be able to bring the guilty to justice. Yet, the Supreme Court's judgement declaring illegal the compulsory use of narco-analysis, brain-mapping and polygraph tests on suspects is hugely welcome as it defends human rights and a fundamental principle of criminal jurisprudence.

The court said that subjecting an accused, a suspect or a witness to such techniques amounted to a violation of Article 20 (3) of the Constitution which prohibits self-incrimination and intrusion of personal liberty under Article 21 of the Constitution.

“We are of the considered opinion that no individual can be forced and subjected to such techniques involuntarily, and by doing so it amounts to unwarranted intrusion of personal liberty,” the bench headed by Chief Justice K G Balakrishnan, and comprising Justices R V Raveendran and Dalveer Bhandari, said.

The court further said that while the investigating agencies could make use of such techniques after obtaining due consent of the accused, the result of the test would still not be an admissible piece of evidence.

The court made it clear that the investigating agencies would have to strictly follow the guidelines laid down by the National Human Rights Commission while conducting the polygraph test.

Those who had moved the apex court included Santokben Sharmanbhai Jadeja, a woman accused of leading an underworld gang in Gujarat, Tamil Film producer K Venkateswara Rao, fake stamp paper scam accused Dilip Kamath and independent Maharashtra MLA Anil Gote.

The Supreme Court had on January 25, 2008 reserved its order on a batch of petitions challenging investigation techniques like brain mapping, lie detection and narco-analysis as being illegal and unconstitutional, especially in cases where accused were opposed to them.

This judgement assumes significance as probe agencies have used narco-analysis, brain-mapping and polygraph tests in a number of high-profile cases involving fake stamp paper kingpin Abdul Karim Telgi, Nithari killings accused and Aarushi murder case suspects as well as parents of the teenager.

The Delhi High Court had recently restrained police from going ahead with narco-analysis test on top Maoist leader Kobad Ghandy in view of the pendency of the legality of such tests in the apex court. However, on May 3, a Rajasthan court had granted the state's Anti-Terrorism Squad permission to conduct narco-test on Devendra Gupta, an accused in the 2007 Ajmer Dargah blast case.

Even Law Commission was of the opinion that such a provision was necessary for effective investigation and it would not affect the fundamental rights, it had said, adding "no invasive procedure is involved" in using modes of investigation like lie detector and the brain mapping tests.

It had argued that the use of narco analysis was of particular relevance in the context of terrorist-related cases, conspiracy to commit murder and other serious offences in which probe agencies got vital leads for follow up action.