The Transformative Role of Scientific Evidence in Criminal Justice

When a crime takes place, the first question investigators must answer is: what actually happened here? Eyewitness accounts help, but they can be unreliable, contradictory, or simply unavailable. What remains – fingerprints on a surface, a strand of hair, a bloodstain, digital footprints – does not forget, does not change its story, and cannot be intimidated. Scientific evidence has fundamentally shifted how criminal justice systems around the world, including India’s, pursue truth. Far from being a supporting tool, it has become a primary pillar of modern criminal trials.

What is scientific evidence in criminal justice? 🔗

Scientific evidence refers to any information gathered through systematic, empirical methods that can be used in a court of law. In the criminal justice context, it is often called forensic evidence – from the Latin forensis, meaning “of the forum” or “of the court.” Forensic science is broadly defined as the application of science to civil and criminal laws enforced by police agencies. It encompasses a wide range of disciplines: DNA analysis, fingerprint examination, ballistics, toxicology, digital forensics, trace evidence analysis, and more. Each discipline contributes a different piece to the puzzle of what happened, when, how, and – crucially – who was responsible.

In India, the formal use of forensic science in criminal investigations has a long history. The country’s first toxicology laboratory was set up in mid-18th century Madras to investigate poison-related deaths, and the first dedicated forensic science laboratory was established in 1952, reflecting an early commitment to science-backed justice. Today, a network of state and central forensic science laboratories (FSLs) supports law enforcement agencies and courts across the country.

Locard’s exchange principle: the bedrock of forensic science 🔗

Every discussion of scientific evidence in criminal justice returns, sooner or later, to one foundational idea. In 1910, French criminologist Dr. Edmond Locard formulated what is now regarded as the cornerstone of all forensic science. His principle – often summarised as “every contact leaves a trace” – holds that whenever a perpetrator commits a crime, they bring something into the crime scene and leave with something from it, and both can serve as forensic evidence.

In practical terms, this means that physical contact between a suspect and a crime scene, a victim, or an object inevitably produces a transfer of material. Hair, skin cells, fibres, soil, pollen, fingerprints, blood, or gunshot residue – all of these are potential carriers of this exchange. When these transferred materials are detected, they establish a connection between a suspect and a crime scene or between a suspect and a victim.

Locard’s principle is not merely theoretical. In a well-known early application, Locard himself examined a murder suspect named Emile Gourbin in 1912 who had an alibi. By scraping beneath Gourbin’s fingernails, Locard found traces of the victim’s makeup powder, proving physical contact and dismantling the alibi. This logic – trace material proves contact, contact proves presence – continues to underpin forensic investigation today. The Indian Supreme Court has also affirmed this reasoning, holding in Narayana Swamy v. State of Karnataka that the mere absence of fingerprints does not negate a suspect’s presence at a scene when other circumstantial evidence exists.

Types of scientific evidence and their role in trials 🔗

Scientific evidence in criminal trials operates across multiple categories, each serving a distinct evidentiary function.

Biological and DNA evidence 🔗

DNA profiling is among the most powerful tools in forensic science. Because no two individuals (except identical twins) share the same DNA profile, a match between a biological sample from a crime scene and a suspect’s profile can be near-conclusive evidence of contact. In India, the landmark role of DNA evidence became widely recognised in the 2012 Nirbhaya gang rape case, where DNA profiling was central to locating and convicting the accused, with biological specimens from the scene compared against the suspects’ profiles. Serological analysis – examining blood, semen, saliva, and other bodily fluids – also plays a critical role, particularly in cases involving sexual offences.

Trace and physical evidence 🔗

Trace evidence refers to materials transferred in small quantities between persons, objects, or locations during a crime. This includes hair fibres, textile threads, paint chips, glass fragments, soil samples, and gunshot residue. These materials are collected, analysed, and compared to establish linkages. The analysis of trace evidence is directly grounded in Locard’s exchange principle, which forms the basis for forensic science as we know it. Even when a criminal tries to cover their tracks, trace materials often survive and tell a story that human witnesses cannot.

Fingerprint analysis 🔗

Fingerprint analysis is one of the oldest and most reliable forms of forensic identification. Based on the principle of individuality – that no two people share identical ridge patterns – fingerprint matching has been used in Indian courts for well over a century. It remains a foundational method for placing a suspect at a scene and is admissible under the Indian Evidence Act framework that governs expert testimony.

Ballistics and toolmark evidence 🔗

Ballistic evidence involves the scientific examination of firearms, bullets, and cartridge casings to determine what weapon was used, from what distance a shot was fired, and sometimes who fired it. Toolmark analysis similarly examines impressions left by tools – such as a crowbar used to force entry – and compares them to specific instruments. These forms of evidence are particularly significant in cases of violent crime involving weapons.

Digital forensic evidence 🔗

As crime increasingly involves digital infrastructure, digital forensics has become essential. This discipline recovers and analyses data from computers, mobile phones, and other electronic devices. In the Tomaso Bruno and Anr. v. State of Uttar Pradesh case, the Supreme Court held that electronic evidence has strong potential as a tool for law enforcement in establishing unquestionable facts. Digital evidence can corroborate or contradict alibis, reveal communication patterns, establish timelines, and trace financial transactions linked to criminal activity.

How scientific evidence functions in a criminal trial 🔗

Scientific evidence serves several interrelated purposes within criminal proceedings – it is not a single-use tool but a multifunctional instrument of justice.

Establishing facts and reconstructing the crime 🔗

The primary function of forensic evidence is to reconstruct what actually happened. Crime scene investigation combines science, logic, and law. Physical material found at the scene – biological traces, objects, impressions – forms a narrative that investigators piece together. Crime scene investigation aims to gather information about what occurred, establishing a clear connection between the victim, the suspect, and the physical evidence.

Identifying suspects and linking them to the crime 🔗

Scientific evidence is often the most objective means of suspect identification. Unlike an eyewitness who may be influenced by stress, bias, or poor lighting, a DNA profile or fingerprint match is not subject to perception errors. Forensic methods help narrow or eliminate suspects efficiently, reducing the risk of wrongful convictions.

Corroborating witness testimony 🔗

Witness testimony remains important in criminal trials, but it becomes considerably stronger when backed by scientific evidence. If a witness says they saw the accused at a particular location, and trace evidence independently places the accused there, the two forms of evidence mutually reinforce each other. Conversely, when physical evidence contradicts testimony, it alerts the court to possible unreliability.

Tracing the crime scene location 🔗

Certain types of trace evidence – pollen, soil, plant matter – are geographically specific and can help place suspects or victims at particular locations. Forensic geology and environmental forensics exploit this characteristic. In cross-border criminal investigations, this function has proven particularly powerful. The 1999 murder of British teenager Hannah Foster was solved partly through traces of pollen and textile fibres found in the victim’s clothing, eventually leading to the arrest of the accused who had fled to India.

Legal framework governing scientific evidence in India 🔗

The admissibility and use of scientific evidence in India is governed by a layered legal framework. Historically, the primary statute was the Indian Evidence Act, 1872, which recognised expert testimony under Section 45, allowing courts to consider the opinions of experts in science, art, foreign law, or handwriting. The Code of Criminal Procedure, 1973 (CrPC), particularly Sections 53 and 54, enabled courts to order forensic examination of accused persons, including the collection of bodily samples.

India’s three new criminal laws – the Bharatiya Nyaya Sanhita (BNS), 2023, the Bharatiya Nagarik Suraksha Sanhita (BNSS), 2023, and the Bharatiya Sakshya Adhiniyam (BSA), 2023 – represent a significant modernisation of this framework. The BNSS, which replaced the CrPC with effect from July 1, 2024, contains a particularly important provision: it mandates forensic investigation for all offences punishable with seven years of imprisonment or more, requiring forensic experts to visit crime scenes and document the evidence collection process electronically. If a state lacks forensic infrastructure, it must utilise facilities from another state. This is a structural shift – forensic evidence moves from being an optional tool to a legal requirement in serious cases.

The BNSS also expanded the scope of biometric collection, allowing Magistrates to order specimen signatures, finger impressions, handwriting samples, and voice samples even from persons who have not been arrested. The Bharatiya Sakshya Adhiniyam, 2023 further strengthens the admissibility of electronic evidence and the framework for expert testimony in courts.

Key principles that support forensic science 🔗

Forensic science is not built on Locard’s principle alone. Several other scientific principles guide how evidence is collected, analysed, and interpreted in court. The principle of individuality holds that every person, object, or substance has unique characteristics that distinguish it from all others – the basis for fingerprint and DNA analysis. The law of progressive change recognises that crime scenes, physical evidence, and offenders all change over time, underscoring the urgency of prompt evidence collection. The principle of comparison requires that like must be compared with like – only comparable specimens yield reliable forensic conclusions. Finally, the law of probability provides the statistical foundation for determining the likelihood that two samples share a common origin, a principle central to DNA evidence interpretation in court.

Challenges in using scientific evidence in India 🔗

Despite considerable progress, the use of scientific evidence in India’s criminal justice system faces real obstacles. Challenges include outdated forensic infrastructure, limited standardisation and accreditation of forensic laboratories, inadequate training for law enforcement personnel, and the absence of clear guidelines for the collection and preservation of forensic evidence. Chain-of-custody failures – where evidence is mishandled between collection and presentation in court – can undermine otherwise strong scientific findings. Courts, particularly at the trial level, sometimes lack the expertise to properly evaluate complex forensic testimony.

There is also the broader problem of judicial unfamiliarity with evolving science. Law enforcement and judges are not always well-informed about modern forensic methods, and there is an absence of precise legal guidelines for incorporating technologies such as AI-based forensic analysis into court proceedings. As a result, even compelling scientific evidence can be contested or discounted if the court lacks the tools to evaluate it properly. Addressing these gaps requires investment in forensic laboratory infrastructure, systematic training, and clearer evidentiary standards.

There is also the constitutional dimension. In Selvi v. State of Karnataka (2010), the Supreme Court ruled that the compulsory administration of forensic techniques such as narco-analysis and polygraph tests – without the subject’s consent – violates the right against self-incrimination under Article 20(3) and the right to personal liberty under Article 21. The Court held that any use of these methods requires the willing participation of the target, drawing a clear boundary between legitimate forensic investigation and coercive practices.

The significance of scientific evidence in modern criminal justice 🔗

The integration of scientific evidence into criminal trials is not simply a technical matter – it is a justice matter. Scientific investigation is considerably more effective and accurate than a criminal justice system built primarily on eyewitness testimony. An offender should not walk free because a witness was unavailable or unreliable, nor should an innocent person be convicted because a witness was mistaken. Scientific evidence creates a more objective, reproducible foundation for judicial decision-making.

India’s new criminal laws signal a clear legislative direction: forensic science is not supplementary – it is integral. As DNA databases expand, digital forensics matures, and AI-assisted analysis enters the laboratory, the precision and scope of scientific evidence will only increase. The challenge for the justice system is to keep pace: building infrastructure, training professionals, and developing legal standards that can accommodate scientific advancement without compromising procedural fairness.

What do you think? Given that the BNSS now mandates forensic investigation for all serious offences, should India also establish a uniform national standard for the accreditation of forensic laboratories – and what would it take to make that a reality? And with scientific evidence increasingly carrying more weight than eyewitness testimony in criminal trials, how should courts balance the authority of forensic findings against the constitutional rights of the accused?

References

1. https://www.ijcrt.org/papers/IJCRT2403015.pdf
2. https://www.mondaq.com/india/crime/1469694/the-role-and-admissibility-of-forensic-evidence-in-the-indian-criminal-justice-system
3. https://en.wikipedia.org/wiki/Locard%27s_exchange_principle
4. https://nij.ojp.gov/library/publications/toward-locards-exchange-principle-recent-developments-forensic-trace-evidence
5. https://www.legalserviceindia.com/Legal-Articles/locards-principle-vs-absence-of-evidence-forensic-legal-analysis/
6. https://www.forensicscijournal.com/journals/jfsr/jfsr-aid1072.php
7. https://www.forensicsciencesimplified.org/trace/principles.html
8. https://prsindia.org/billtrack/the-bharatiya-nagarik-suraksha-sanhita-2023
9. https://www.lexology.com/library/detail.aspx?g=add91fba-71e4-4069-809c-6339b64bd9ed
10. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4565177
11. https://ijlmh.com/paper/law-of-forensic-evidence-in-india-and-abroad-a-comparative-study/