Forensic Tools for Eyewitness Testimony Assessment in India

Criminal investigations in India often hinge on eyewitness testimony – but what happens when that testimony is unreliable, inconsistent, or possibly deceptive? This is where forensic psychologists step in, armed with a set of specialized tools designed to assess the truthfulness and accuracy of statements made by eyewitnesses and suspects. India has developed and adopted several forensic techniques – including polygraph tests, Brain Electrical Oscillation Signature Profiling (BEOSP), and narcoanalysis – that play a growing role in the country’s investigative process. Each of these tools operates on distinct scientific principles, follows specific procedural protocols, and carries its own set of strengths and limitations.

Why forensic tools matter in Indian investigations 🔗

India’s criminal justice system has long grappled with the challenge of extracting reliable information from uncooperative or deceptive individuals. Traditional interrogation methods have often been criticized for relying on coercion, which not only violates human rights but also produces unreliable results. According to the Indian Journal of Medical Research, deception detection tests (DDTs) such as the polygraph, narcoanalysis, and brain mapping have emerged as alternatives that claim to be safer and more scientific than third-degree methods. These tools help forensic psychologists systematically evaluate whether a witness or suspect is concealing information relevant to a criminal case.

These forensic techniques are used across several Forensic Science Laboratories (FSLs) in India, including prominent ones in Gandhinagar (Gujarat), Mumbai, Chandigarh, and Bangalore. Importantly, all of these tools are language-independent, meaning they can be administered in any language – a crucial advantage in a country with hundreds of dialects and regional languages.

Polygraph test (lie detector test) 🔗

The polygraph is the oldest and most widely used deception detection tool in forensic psychology. It has been in use since the 1920s and remains a standard instrument in criminal investigations worldwide, including India.

How the polygraph works 🔗

The polygraph operates on a straightforward principle: when a person lies, their body produces involuntary physiological changes. The test measures several bodily responses simultaneously using multiple sensors. These include pneumograph sensors that track changes in abdominal and thoracic respiration, a sphygmomanometer (blood pressure cuff) that records blood pressure and pulse variations, and an electrodermal activity (EDA) sensor that monitors changes in skin conductance caused by sweat gland activity. Modern polygraphs also include countermeasure sensors – such as pressure gauges placed on the seat and under the hands and feet – to detect if the subject is trying to manipulate the results through deliberate physical movements.

Procedure and questioning techniques 🔗

A polygraph examination typically involves three phases: a pre-test interview, chart recording, and diagnosis. During the pre-test phase, the examiner – usually a clinical or forensic psychologist – explains the procedure and prepares a set of questions based on the case details provided by the investigating officer. There are three main questioning techniques used: the Relevant-Irrelevant (R-I) technique, the Control Question (CQ) technique, and the Directed Lie-Control (DLC) technique. During chart recording, the subject’s physiological responses are captured while they answer the questions. The examiner then analyzes the charts to determine whether deception was indicated.

Limitations and legal standing 🔗

Despite its widespread use, the polygraph has significant limitations. The physiological changes it measures – increased heart rate, elevated blood pressure, sweating – are not exclusive indicators of deception. They can also be triggered by nervousness, anxiety, confusion, or even medical conditions. As noted in a study published in the Indian Journal of Medical Research, a trained individual can potentially defeat a polygraph test by using relaxation techniques, yoga, or meditation to suppress arousal symptoms. In India, polygraph results are not admissible as standalone evidence in court. The landmark Supreme Court ruling in Selvi v. State of Karnataka (2010) established that polygraph tests cannot be administered without the voluntary and informed consent of the individual.

Brain Electrical Oscillation Signature Profiling (BEOSP) 🔗

BEOSP – also referred to as BEOS or sometimes loosely as “brain mapping” – is an indigenous Indian forensic tool that represents one of the country’s most notable contributions to investigative psychology. It was developed by Professor C.R. Mukundan, a neuroscientist and former head of Clinical Psychology at the National Institute of Mental Health and Neurosciences (NIMHANS) in Bangalore.

The science behind BEOSP 🔗

BEOSP is based on a core neuropsychological principle: the human brain reacts differently to information it has personally experienced compared to information it has only heard about or read. The technique distinguishes between primary encoding – deep-seated memory formed through direct personal participation in an event – and secondary encoding – knowledge acquired indirectly through conversations, media, or books. BEOSP aims to identify whether a suspect possesses “experiential knowledge” of the crime, meaning first-hand memory of having participated in or witnessed the criminal event.

The tool uses electroencephalography (EEG) to record the brain’s electrical activity. A cap with 32 electrodes is placed on the subject’s head, and the system records brain wave patterns across multiple channels while stimuli related to the crime are presented.

How the test is conducted 🔗

The procedure is notably different from the polygraph. The subject is not asked any questions and does not need to speak or respond at all. Instead, short statements called “probes” are presented to them in a sequential and chronological manner through audio playback. Each probe is presented only once. These probes are crafted from case-specific details – drawn from the FIR, post-mortem reports, crime scene photographs, and the investigating officer’s case summary.

The system then analyzes changes in brain wave patterns in response to each probe. The software classifies these responses into categories including Experiential Knowledge (EK), which indicates remembrance of personal experience triggered by the probe; Emotional Response (EM); No Encoding (NE); and other classifications. If the analysis indicates the presence of experiential knowledge, it suggests the subject has first-hand involvement with the events described in the probes.

Use in Indian cases 🔗

BEOSP has been deployed in over 700 police investigations in India. The technology is currently used in Forensic Science Laboratories in Mumbai, Gandhinagar, and Chandigarh. It has featured in several high-profile cases, including the Nithari serial killings, the Aarushi murder case, the Godhra train burning case, and the Hathras case. In one notable instance – a 2008 Pune sessions court case – an accused was convicted of murder based significantly on BEOSP results, making it one of the few cases globally where such technology directly contributed to a conviction.

Limitations and legal position 🔗

Despite its extensive use, BEOSP is not without controversy. The published scientific literature on the technique remains sparse, and researchers have raised concerns about the lack of large-scale, peer-reviewed validation studies. The Indian Supreme Court, in the Selvi v. State of Karnataka (2010) ruling, clarified that brain mapping tests – like the polygraph and narcoanalysis – cannot be forced on any individual without their consent. The results of BEOSP can be accepted as corroborative evidence under Section 45 of the Indian Evidence Act, but they are not sufficient on their own to secure a conviction. A court order and the subject’s informed consent – obtained twice, once in court and again at the forensic laboratory – are mandatory before the test can proceed.

Narcoanalysis (truth serum test) 🔗

Narcoanalysis is perhaps the most controversial of the three major forensic tools used in India. It involves administering a controlled dose of a psychotropic drug to lower a subject’s inhibitions, placing them in a state where they are believed to be more likely to reveal concealed information.

How narcoanalysis works 🔗

The term “narcoanalysis” derives from the Greek word narke, meaning numbness. The technique involves injecting a barbiturate drug – most commonly sodium pentothal (also known as sodium thiopental) – intravenously. This drug acts as a central nervous system depressant. It lowers blood pressure, slows heart rate, and induces a hypnotic or semi-conscious state. The dosage is carefully calibrated based on the subject’s age, sex, weight, and overall health, because administering too much can lead to unconsciousness or even coma, while too little allows the subject to maintain enough self-control to resist questioning.

In this twilight state between consciousness and sleep, the subject’s ability to fabricate or withhold information is believed to be significantly reduced. When the person begins to become drowsy and starts fumbling their words, the forensic psychologist conducting the session begins the questioning.

Procedure and team involved 🔗

Narcoanalysis is conducted by a multidisciplinary team that includes a forensic psychologist (who leads the questioning), an anaesthesiologist (who administers and monitors the drug), a psychiatrist, a general physician, and supporting nursing staff. A language interpreter may also be present if needed. A videographer records the entire session on audio and video for later scrutiny. In India, the test is typically performed either inside a Forensic Science Laboratory or in the operation theatre of a recognized hospital.

The standard protocol involves mixing approximately 3 grams of sodium pentothal dissolved in 3000 ml of distilled water. This mixture is administered intravenously along with 10% dextrose over a period of about three hours, with the anaesthesiologist carefully controlling the rate of administration. The forensic psychologist works closely with the investigating officer beforehand to prepare case-specific questions.

Reliability concerns 🔗

Narcoanalysis carries significant reliability issues. The drug does not guarantee truthful responses – subjects may mix actual memories with fantasies, imagination, or irrelevant personal details. Some individuals are able to maintain their capacity to deceive even under the drug’s influence, while others become excessively suggestible. This means investigators could inadvertently prompt incriminating responses through the way they frame questions. As the Indian Journal of Medical Research notes, the statements made during narcoanalysis are neither voluntary nor made in a clear state of mind, which fundamentally undermines their evidentiary value.

Legal position in India 🔗

The legal standing of narcoanalysis in India has been shaped primarily by two rulings. The 2010 Selvi v. State of Karnataka judgment declared that narcoanalysis, like the polygraph and BEOSP, cannot be administered involuntarily. The Supreme Court held that forced administration violates both Article 20(3) (right against self-incrimination) and Article 21 (right to life and personal liberty) of the Indian Constitution. More recently, the 2025 ruling in Amlesh Kumar v. State of Bihar reaffirmed these protections, setting aside a High Court order that had permitted narcoanalysis of the accused without proper consent. Under Section 27 of the Indian Evidence Act, any information or material subsequently discovered based on voluntarily obtained narcoanalysis results can, however, be admitted as evidence.

Other emerging tools 🔗

Beyond the three major techniques, Indian forensic psychologists also employ a few additional tools worth mentioning.

Suspect Detection System (SDS) 🔗

The SDS is a streamlined screening tool that uses only one sensor – the electrodermal activity (EDA) sensor – to detect changes in skin conductivity when a suspect is presented with crime-related questions. The questioning technique mirrors that of the polygraph, using the Concealed Information Test (CIT) or Guilt Knowledge Test. Because it requires only a single sensor and less time, it is particularly useful for quickly screening multiple suspects in the early stages of an investigation.

Layered Voice Analysis (LVA) 🔗

Originally developed in 1997 by Amir Liberman, LVA analyzes subtle emotional cues embedded in a person’s speech. It detects variations in stress, excitement, confusion, and other emotional states by identifying patterns and anomalies in the speech flow. LVA can work both in real time and on pre-recorded audio, making it a flexible tool for forensic settings. It is used in several Indian FSLs for suspect screening, though it primarily serves as a supplementary rather than primary investigative tool.

The legal and ethical framework 🔗

All forensic psychological tools used in India are governed by strict legal and ethical safeguards. The National Human Rights Commission (NHRC) Guidelines, first published in 2000, set the procedural standards for administering deception detection tests. These guidelines mandate that no test can be administered without the subject’s voluntary consent. The subject must have access to a lawyer, be informed of the physical, emotional, and legal implications, and the consent must be recorded before a Judicial Magistrate.

The overarching legal principle, reinforced through the Selvi judgment, is that the results of these tests are not admissible as standalone evidence. They serve as investigative aids – tools that can generate leads, provide corroborative support, or guide the direction of an investigation – but they cannot, on their own, prove guilt. This balance reflects the Indian judiciary’s effort to embrace scientific methods while protecting the constitutional rights of individuals.

Contributions to the investigative process 🔗

Despite their limitations, these tools have made meaningful contributions to criminal investigations in India. In cases where physical evidence has been destroyed or is simply unavailable, techniques like BEOSP and narcoanalysis have helped uncover new leads and direct investigations toward productive avenues. They have been used in terrorism cases, organized crime, serial killings, and other serious offences where conventional methods have reached a dead end.

The fact that all of these tools are language-independent is a particularly significant advantage in the Indian context, where a single investigation might involve witnesses and suspects who speak different regional languages. These tools eliminate linguistic bias from the assessment process, allowing forensic psychologists to evaluate individuals fairly regardless of their mother tongue.

What do you think? Given that none of these forensic tools produce results admissible as standalone evidence, do you believe India should invest more in developing newer, scientifically validated tools – or should the focus shift toward improving traditional investigative methods? How do you think the balance between technological advancement and individual rights should be maintained in criminal investigations?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC3171915/
2. https://forensicfield.blog/investigative-tools-in-forensic-psychology-in-india/
3. https://indiankanoon.org/doc/338008/
4. https://en.wikipedia.org/wiki/Brain_Electrical_Oscillation_Signature_Profiling
5. https://www.legalserviceindia.com/legal/article-6680-brain-electrical-oscillation-signature.html
6. https://thelawmatics.in/narcoanalysis-technique-origin-procedure-and-admissibility-in-law/
7. https://www.prashantkanha.com/narco-analysis-constitutionality-in-india-2025-supreme-court-ruling-on-consent-rights-and-legal-admissibility-explained/