Legal Admissibility of Deception Detector Tests in India
By Shweta Nair
Crimes in the society are ever-increasing. Whenever we open and read newspaper, we find
that there are new types of crimes being committed every day. In short, criminals as well as
crimes both are advancing according to the changing times with better techniques in-hand.
Along with it, following third degree methods like imposing torture and mental or physical
pain in order to retrieve information by the police won’t work presently in dealing with extra
smart scientific and technologically proficient criminals. Even the police interrogation and
investigation methods must advance along with criminals and crime in order to tackle it
rightly. For that, newer techniques with the help of forensic science like the polygraphy test,
brain mapping and narco analysis have been developed and adopted. It assists the police and
investigating officers greatly in exposing the lies and in interrogating a criminal.
Polygraphy test is an instrument used to detect whether a person is telling the truth or a lie.
Here few instruments are attached to the body of the suspect and while the questions are
being asked, the instrument records the physiological responses like heart rate, blood
pressure, respiration, skin conductivity etc. The theory states that an individual while lying
produces a different physiological response. Though it looks extremely simple in theory, its
quite difficult to say that such test is completely accurate since it contains its own pitfalls. It
has been observed that nervousness or anxiety or fear could also bring a change in
physiological responses and not only lying. Also, such instruments can be manipulated by the
suspect by controlling their responses. Many times, offenders do so by squeezing muscles of
one’s posterior or by fake sneezing. The mental state of the suspect is important during the
test, if he or she is depressed the results may be distorted. Even the condition of the room
affects the results.
There are other methods too which police and investigating officers rely upon and that is by
narco analysis and brain mapping. Narco Analysis takes place by using injecting
psychotropic drugs like pentothal sodium which results in an anaesthetic effect and the
suspect goes into a hypnotic trance state making it simpler for interrogation as its believed
that in such a sleep like state the suspect will bring out the hidden information in his mind.
However, such a technique also cannot provide 100% accuracy as there is no guarantee
whether the offender can deceive using such technique, mostly by those who are expert liars
and became flexile with answering questions. It may also result in incriminatory replies.
Even the brain mapping method which measures electrical waveforms emitted by the brain
by showing pictures or videos or any other words related to crime scenes in order to gauge
how the brain responses to particular stimuli in comparison with irrelevant stimuli. Such a
test can also lead to inconsistencies as it depends upon the familiarity concept and knowledge
of a particular crime may also be due to media or may be if he was an eyewitness to the crime
and not necessarily that he himself committed it.
Even though National Human Rights Commission had provided guidelines for administering
such tests- for example the consent of the accused being mandatory before taking test in order
to protect his rights yet many times these are not followed properly. None of the above
Deception Detector Tests are admissible as evidence in any court as per the Supreme Court as
it was observed that such tests infringe Article 21(3) of the Indian Constitution which forbids
an accused person from being witness against himself. Here the accused is not giving answers
voluntarily as he cannot choose to answer it or not thus violating his fundamental right.
Besides, there is scientific uncertainty pertaining to its usage as such tests work to bring out
the concealed information from him and due to fear or anxiety, it may show deceptive results
which also risks an innocent person to be found guilty. Thus, Supreme Court has held that
such tests clearly intrude upon the rights of the accused against self-incrimination and
substantive due process rights.
Though it cannot be taken as evidence yet it can be looked upon as a professional opinion
under the Evidence Act. Thus, such tests though help in detecting lies and are helpful to the
investigating authorities yet it cannot be admissible in court as it violates personal liberties.