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The truth of lie-detection test

delhi Updated: Feb 11, 2017 00:14 IST
1984 riots

A woman during a protest against Jagdish Tytler for his alleged role in 1984 riots. The CBI has sought court’s permission to conduct a lie detector test on Tytler.(Raj K Raj/HT Photo )

Lie-detection test in a three-decade-old case? Even if it relates to a relatively recent charge, that the accused manipulated witnesses to the original crime, what’s the value of the evidence that isn’t conclusive?

The questions acquire relevance with the CBI wanting Congress leader Jagdish Tytler to undergo a lie-detection test in a case relating to the 1984 anti-Sikh riots. The agency says arms dealer Abhishek Verma, who has accused Tytler of influencing witnesses in the case, be similarly tested.

A law the Supreme Court laid down in 2010 makes the accused person’s consent mandatory for the test. It’s for that reason the court directed the Tylter-Verma duo to appear before it in pursuance of the CBI plea.

Investigators and lawyers have identical positions on the limited value of the Polygraph Examination and Brain Electrical Activation (BEAP) test. Senior Delhi High Court lawyer Ramesh Gupta says the procedure helps investigators to eliminate doubts. It’s not meant for “inclusion” of evidence.

“The report at best gives assurance to the police that they’re moving in the right direction,” he surmised. For example: blood samples found on the scene of the crime matching the accused person’s blood group isn’t conclusive evidence that can only be obtained through a DNA test that’s the next step.

Even the SC judgment on BEAP clarified the position by referring to section 27 of the Evidence Act that, when deciphered in layman terms, means that tangible objects recovered on the basis of the test would be admissible as evidence in the case. Example: stolen property found on the strength of the test shall be admissible without it being construed as admission of guilt.

Agreeing broadly with Gupta’s line of argument, a one-time crack investigator of Delhi Police said lie-detection was “an indicative, not conclusive test the value of which before a court has its constraints.” For a clearer picture of the difference, he compared polygraph with finger print tests that have conclusive evidentiary value.

Unwilling to be quoted as the case under discussion has political dimensions, the police officer claimed that at times, probe agencies resorted to polygraph to ward off pressure. Adumbration: media coverage of the test gave the impression of work happening on the case.

Honourable exceptions are indeed there. When deployed as an investigative tool and not a diversion, contradictions that get thrown up in lie tests on accused persons, or on witnesses, are dissected in rigorous, follow-up interrogations. That could, at times, mean confronting them with another version of the crime or the circumstances leading to it.

“Good investigators,” insisted the former detective, “rely on detailed, tactful interrogation, not as much on tools such as BEAP….” So if Messrs Tytler and Verma do submit to the test, its results would need to be verified by other means.