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This article is written by Prateek Mudgal, from Faculty of Law, Aligarh Muslim University. The article deals with various psychiatric and scientific methods of investigation. In this article, I have dealt with deception detection tests which include narco-analysis, polygraph and brain mapping. The article has also given references to landmark cases and recent cases, in the end, the use of hypnosis in an investigation is dealt with in detail.


With growing technology, various new changes are arriving in various fields. Fields are struggling to keep their pace with new methodologies, not only technological advancements are behind such changes, but the application of these in varied fields. The legal field also has seen several changes, be it cyber laws, laws related to IPR or laws related to artificial intelligence. Apart from these legislations there surely will be changes in the procedural laws as well. Covid-19 has seriously made a significant change in the working culture, who would have thought that work from home is possible, but it is. Similarly, a lot of changes are coming in the method of investigation and methods, in this article, I will deal with such methods of investigation and will also discuss the cons and pros along with the use of hypnosis in the criminal investigation.

Deception detection tests

Deception detection tests or DDTs are scientific and psychiatric tests that are being used to detect lies or to gather some important information. Apart from this DDTs are also used to gain a lead in the case, or in cases when the potential witness is unable to gather information, it is also used sometimes on the suspect, the use of DDTs on suspects can have varying effects. DDTs include the use of Narco-Analysis, Polygraph Test, and Brain-mapping. What we have to understand is that the use of DDTs in criminal investigation raises a few pertinent questions from medical, ethics as well as the legal field. Therefore, the use of DDTs in the criminal investigation cannot be thought of as an isolated event but must be watched out as a dependent cause and effect event, which affects other fields as well.

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Scientific description of DDTs


In narco-analysis intravenous drugs are administered, because of which the individual passes through various stages(degrees) of consciousness. One such stage of consciousness is called the hypnotic stage. In this stage of hypnosis, the subject divulges that factual information, which in their consciousness they would have not. Apart from this the subject also reveals his misinterpretations, fantasies, wishes and other information which might be relevant or irrelevant depending on the information provided. The major drawback of this is, even during the hypnotic stage a few manage to lie, and in some cases, the subjects become very suggestible thus prone to be swayed away.

Issues surrounding narco-analysis

When narco-analysis is used without consent several issues arise, hereafter I will mention a few such issues which are as follows:

  1. Issue of assaulting physically the person in hypnotic stage, the assault may involve anything ranging from a slap to shaking the body. Such an issue arises because it becomes necessary to continuously wake-up the subject under hypnosis to answer the question. Other injections, which are painful, also come under physical assault.
  2. Apart from physical assault, mental assault cannot be ignored. When such a drug or injection is administered, it may affect how a person responds mentally and may be counted as a mental assault. Apart from this in the hypnotic stage, the subject divulges a lot of private information, this means that narco-analysis also trespasses the privacy of the subject.
  3. Apart from this, there is a lot of debate in the medical fraternity and this method has not shown sufficient results in treating any psychiatric problem. This technique has been known for quite some time now, but academic research to back the claim of hypnosis are very few. 


The most commonly used misnomer for polygraph is the lie-detecting machine. Though it helps in a similar way but to name it so would be quite ignorant. In the world of Netflix and web-series, it may be known on what principle does the polygraph work, but still, it is important to give an overview of the working of Polygraph tests. Polygraph tests work on the theory that when a person lies about a particular subject he does not act naturally and enters a state of hyperarousal, in which various bodily functions work in a different way than normal. Such different behaviour is noted and recorded by the polygraph and a person who is skilled at reading the readings of polygraph may help to know the instances where individuals lied. Several parameters are involved in giving out the readings, this involves: 

  • A sudden change of heart rate,
  • A subtle change in blood pressure,
  • Change in breathing or respiratory rate.

These are not the only changes. Other changes are also seen which include complex terms like electromyography.

Reliability of polygraph

Polygraph technique can be very beneficial, but is it accurate and precise? Accuracy and precision of the polygraph test are doubtful. Let’s understand why.

  • The major issue arises, because of the principle on which the polygraph test is based, that is the change in bodily functions, such changes can have other reasons than lie as well. For instance physical or mental problems like anxiety, stress, fear, getting nervous, suffering from depression, or other emotions can affect the bodily functions and give an unreliable reading of the polygraph test. Therefore it becomes clear that there may be aberrations in the reading due to above-mentioned problems and not just lying.
  • Other factors like the environment where the test is conducted, how the questions of investigating officers were and what tone he used, also play a significant role in swaying the reading of the polygraph test.
  • Polygraphic test results can be beaten by individuals with the ability to suppress the arousal response, such ability is gained by those who perform relaxation exercises like Yoga or meditation.

Therefore reliability on polygraph is doubtful, in certain cases it might prove beneficial but in some cases, it may also provide the agencies with incorrect information. Therefore such tests cannot be produced as evidence in the courtroom.


It is one of the most frequently used methods in the investigations, before dealing with the intricacies of this method it is important to understand why it is used and what benefits can be accrued therefrom.

Sensors are attached to the head of the suspect during brain-mapping, the suspect is then made to sit on the chair in front of a computer screen. After these, images related to the crime scene are shown, and audios related to crime are made audible to the suspect. The sensors see the pattern of brain activity and if the suspect is familiar with the image or sound then sensors record the data. This all happens because our brain works differently while seeing or hearing a familiar scene or voice.

Working of brain-mapping

Brain-mapping works by measuring the electrical potential difference, which arises due to the neuronal activity of the brain. Our brain reacts differently to various events, how it reacts to familiar events is different from how it reacts to unknown events. The method used in India is also called the P300 waves test.

During the test, both familiar and unfamiliar auditory as well as a visual stimulus are given and since the brain reacts differently to the familiar one a pattern is observed and accordingly reports are made.

Reliability of brain-mapping

Brain-mapping is surely an advanced method of investigation, apart from being technologically advanced it also is helpful in various ways. But again, like other methods brain-mapping has also certain drawbacks.

  • Since brain-mapping can only be used to measure the knowledge, awareness of an individual with certain visual or audio may lead to suspicion. For instance, if an individual was present at the crime scene or who has vaguely noticed something may be brought under suspicion using this method.
  • Another issue that arises is, there is a lack of information regarding the impact of criminal scenes on television, media or movies. Such memories may also hamper the process of brain-mapping, therefore such a method might not be used as a method to prosecute someone but can be used as a method to prove one’s innocence.
  • Insufficiency of information and data regarding brain-mapping does not stop here. Even in academia, the information present on brain-mapping is very scarce. Scarcity of published literature on brain-mapping is very disappointing to note. 
  • A few pieces of research and studies are going on regarding the functional use of brain mapping imaging, but such researches are inconclusive and therefore the researches have opined against producing brain-mapping results as a piece of evidence in the court.

The stand of authorities regarding DDTs

Investigating agencies have been using DDTs for some time now, and according to the agencies, results are much better than expected. What has to be pointed out here is that information collected through the application of DDTs cannot be presented as evidence itself during the trial. The investigation agencies use the DDTs, to gain delicate information regarding the case, which helps to accelerate the investigation. Apart from this it also provides significant lead to agencies which facilitate case solving.  According to authorities, the use of DDTs is much humane, easy and effective than third-degree methods. Agencies have contested that use of DDTs will fasten the pace of investigation which will lead to quicker judgements, which will lead to speedy proving of guilt and speedy acquittal of innocent.

Conflicting stance

What becomes the matter of contention is, can such methods be legally incorporated into practice by the police? As mentioned earlier that use of DDTs is not merely a legal issue but is more than a legal issue, therefore another question is if the use of DDTs during investigation threatens the natural rights of a person and if it is ethical to be used. It is quite obvious that information and investigation of the accused are necessary and there should be some stringent methods to make the accused talk. If the accused remains silent on the pertinent questions using his legal privilege to outsmart the objective of the constitution, then it becomes necessary to coerce and force the accused to talk. Police brutality and torture are vehemently criticised, but it has to be seen that some powers have to be granted to the police to deal with criminals.

Third-degree treatments and police brutality surely appear strange in the civilised world, but does it appear the same to the prime suspect of a heinous crime as well? Nevertheless, what may be understood is that with growing technology a few methods like DDTs which provide an alternative to such brutality may be used.

Hypnosis and investigation

Hypnosis is often thought of as a cheap magic trick, or if not that then surely the hypnotic Pokemon comes to mind. There is an ongoing debate regarding hypnosis in the scientific community, a few favour a few stand against. When there is such disagreement in the scientific community regarding hypnosis it becomes necessary to understand what hypnosis is.


Hypnosis is nothing but in very simple terms a psychological state in which one person is under psychological control over another person’s mind. The level of control is a vague phraseology but it is a matter of contention as to what amount of psychological control is exerted. It is often compared to a sleeping state, but it is considered that during hypnosis there is a certain amount of consciousness and awareness. The solution we expect from hypnosis is due to increased suggestibility, sadly suggestibility and sensitivity are so increased at times that hypnosis becomes a problem. 

The name of the study where legal complexities meet the chaotic cosmos of psychiatry is called Forensic psychiatry.

Forensic hypnosis

When hypnosis is used in a criminal investigation then hypnosis is called forensic hypnosis. Forensic hypnosis is used to make witnesses or victims recall the details of crime, environment and other subconscious details, which might have been forgotten or are not clear enough to help in the course of the investigation. It is a matter of concern that forensic psychiatry has been extended to accuse or say the individual who is the perpetrator of the crime. Extensive research has been done regarding the state of mind called hypnosis, and there is plenty of disagreement to be able to reach some conclusive grounds. Undoubtedly, the use of hypnosis in the clinical field has been considered helpful as the researches have shown that Hypnosis is of considerable usefulness to bring out the repressed memories.

What has to be kept in mind is medical hypnosis and forensic hypnosis are completely different, apart from this the motive behind both the hypnosis is different as well, therefore there remains a considerable doubt regarding forensic hypnosis.

Circumstances in which forensic hypnosis should be used

Forensic hypnosis as a method shall be used to get a lead in the criminal case, therefore only such people who can give some lead in the case should be brought under forensic hypnosis. Witnesses should not be brought under forensic hypnosis, though when critically needed, forensic hypnosis may be used on potential witnesses. Suspects should not be investigated. Why should we be selective regarding the use of forensic hypnosis? 

Drawbacks of hypnosis

  • Reliability of hypnosis is quite uncertain. During hypnosis, the subject may be unclear regarding reality and fantasy and at times it might be possible that the subject may believe in false to be the truth and therefore fail to realise what actual truth is.
  • No hard and fast rule of making sure if the subject has spoken truth or has presented a story of his version of the truth. Since during hypnosis certain things settle as if were true, it becomes hard for the subject himself to differentiate let alone the investigator.
  • Increased suggestibility of the subject is yet another issue. Apart from this, the drug administered for hypnosis does not guarantee that the subject will speak the truth only. Retention of the ability to deceive is also another issue.

Guidelines concerning the use of hypnosis

If hypnosis as a method is to be used in criminology then certain guidelines are to be considered, these guidelines were suggested by Orne in 1979. The few points to be considered are:

  • Only a psychiatrist or psychologist with special training should use the hypnosis technique.
  • Only very basic facts should be shared with the psychiatrist, this will not let the opinion of the psychiatrist get biased. Any knowledge, which may make the psychiatrist biased regarding the suspect has to be concealed.
  • The psychiatrist also has to be an independent consultant.
  • Proper consent of the subject must be taken before use of any such technique, therefore the psychiatrist must take such necessary measures.
  • Care must be taken by the psychiatrist, that the psychiatrist does not hypnotise the suspect or the accused as it is not beneficial to hypnotise the prime suspect and accused because they may become suggestible and may create an imagined reality.
  • The individual who is hypnotised should not be granted immunity from being prosecuted.
  • After a full and proper evaluation of the medical and psychological condition of the subject, the psychiatrist may commence the hypnosis.
  • The psychiatrist must avoid giving any clues to the subject, otherwise, the subject may get suggestible and the whole purpose of hypnosis gets sidelined.
  • To avoid unnecessary interruption and cueing the investigation should take place in a closed room, only with the subject and psychiatrist present in the room.
  • Information obtained from the subject should not be considered the final word but only hearsay and on this basis police should gather evidence. Only Those collected evidence can be put before the court, and the statements of subjects under hypnosis would not be admissible as evidence in the court.

Admissibility of evidence

As discussed above, it becomes clear that not only the process of hypnosis should be done with proper care, but also the information obtained through investigation should be dealt with caution. If in a case investigation using hypnosis takes place then only under exceptional circumstances the subject should be presented as a witness before the court. Pieces of evidence, statements and other information gathered with the help of hypnosis are considered unreliable and are not admissible evidence. In the UK, under Section 78 of the Police and Criminal Evidence Act 1984, it has been considered that if a police records statement of an individual under hypnosis will likely be ruled inadmissible by the court.

Judgements regarding DDTs

In one of the landmark judgements, the court had expressed its assent to the use of scientific methods during the investigation. In Dinesh Dalmia v. State., the Madras Highcourt ruled that the investigation should be completed within the time-frame and any delay in the investigation will be of benefit to the accused. Apart from this, it was also ruled that if the accused fails to cooperate in the investigation then scientific methods can be used to find out the truth surrounding the crime.

It is not the only case in which the court has opined in favour of scientific methods to be used during the investigations. In another case, Sh. Shailendra Sharma vs State, a similar stance was taken by the court and it was held that such scientific methods aid in the investigation and can be of great utility. What is to be noted is that the court further added that since such scientific methods increase the pace of the investigation they become a necessary aid at times and can be used. It is also to be noted that with an increase in crime in society, such methods and growing technology is required.

Regarding the constitutional validity, the court is of the opinion that by use of these scientific methods, no constitutional infirmity arises. Such methods only help in the investigation, and if any incriminatory statement comes to the surface during the investigation, even then the prosecution cannot rely on that statement and the same cannot be produced as evidence. In the same case of Sh. Shailendra Sharma, it was also held by the court that, if such narco-analysis test is being used then such tests should be within a specified time frame.

Going through the above two case laws, it becomes very clear that these judgments have acquiesced to the use of narco-analysis. Now it would be a treat to know whether a similar stance has been taken in recent judgments or not.

Recent Judgments: a change with time

Previous judgments have very clearly accepted the use of DDTs in the investigation and the reasoning behind doing so was also clearly mentioned. But now the stand of the Supreme Court on DDTs has been completely different. To understand the change it is important to discuss a very important case that helped in making the necessary changes. 

Smt. Selvi & Ors Vs State of Karnataka

In this case, a completely different stand was taken by the supreme court.


In this case, review petitions were filed by the petitioners regarding the use of DDTs (without consent) during an investigation on suspects and witnesses. The reasoning for use of such methods has been similar as mentioned in landmark judgements dealt with just above.

Legal issues

  • Whether the use of DDTs without consent violates Article 20(3) of the Constitution.
  • Whether the use of DDTs increases the chances of self-incrimination.
  • Whether the use of DDTs violates the personal liberty of the subject which is protected by the constitution under Article 21

Key points of judgement

  • Use of DDTs without consent (involuntary administration) violates Article 20(3)of the Indian Constitution, Article 20(3) of the Constitution deals with the right of an individual against self-incrimination. It means that an individual cannot be forced to be a witness against himself.
  • Use of DDTs without consent (involuntary administration) violates the principle of personal liberty and privacy protected under Article 21 of the constitution. (Personal liberty is infringed when the person is confined against his will and the drugs are administered. Mental privacy is breached when under the influence of drugs the subject is made to acknowledge something, that in the conscious state they would have denied).
  • Use of DDTs without consent violates basic human rights. Referring to the judgment in D.K. Basu vs. the State of Bengal, where prevention of inhumane and degrading methods of investigation with any person in custody was stressed upon, same was decided.

Professional ethics of medical practitioners is also questionable in such cases because the administration of such drugs without consent violates basic human rights. This issue was raised before the National Human Rights Commission, and in concerning the same commission issued guidelines in 2000 which concerned the ethics of administration of such drugs.


With the change in time, technological changes are inevitable. Science and reason are bound to flourish, but will it grow towards evolution or destruction are still one of the major issues. With these scientific developments, the effect on other fields is obvious, and in a field like Law which touches almost every sphere of a citizen, Law cannot remain insulated. In the same light, the legal field has witnessed a variety of changes, new legislation and amendments all in order to cope with recent developments in the lifestyle of the common man. Such changes involve legislation regarding cyber laws development of IPR, all these are examples of such changes which the legal field coped with a scientific approach. But often in the rat-race, we lose our conscience and in blindness, we welcome every scientific approach. DDTs are such an example, no doubt it can be of great help, but in thinking the pros we must not forget that at the same time use of DDTs can be of great trouble as well. Previous judgements of courts have allowed the use of DDTs as it helps in the investigation, but recent judgements have made it clear that they violate constitutional values also. The question is should we think beyond the constitution for true justice or the constitution alone is the justice in true senses.


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