Innovations in Biotechnology and Medical Sciences

DNA Analysis in Criminal Cases: Ensuring Credibility and Admissibility


From UPSC perspective, the following things are important :

Prelims level: DNA analysis applications

Mains level: DNA analysis in criminal investigations and and issues

Central Idea

  • The recent judgments by the Supreme Court have raised concerns about the admissibility of DNA reports as conclusive evidence in criminal cases. Highlighting issues of suspicion, lack of examination of underlying findings, and reliable application of techniques, the Court has emphasized the need to establish a robust framework for the acceptance of DNA analysis.

What is DNA analysis?

  • DNA analysis, also known as DNA profiling or DNA testing, is a scientific method used to identify and analyze genetic material present in an individual’s cells.
  • It involves examining specific regions of DNA to create a unique DNA profile for identification purposes.
  • DNA analysis is widely used in forensic investigations, paternity testing, ancestry research, and other fields where genetic identification is required.

Facts for prelims: Basics

Characteristic DNA RNA
Structure Double-stranded Single-stranded
Sugar Deoxyribose Ribose
Bases Adenine (A), Thymine (T), Cytosine (C), Guanine (G) Adenine (A), Uracil (U), Cytosine (C), Guanine (G)
Base Pairing A-T, C-G A-U, C-G
Primary Function Stores genetic information Transfers and expresses genetic information, protein synthesis
Types of RNA Not applicable Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA)
Presence in Viruses Yes Yes
Stability Relatively stable More prone to degradation

 The process of DNA analysis

  • Sample Collection: Biological samples such as blood, saliva, semen, hair, or tissues are collected from the individual or the crime scene.
  • DNA Extraction: The collected sample undergoes a process of DNA extraction, which involves isolating the DNA from other cellular components.
  • Polymerase Chain Reaction (PCR): PCR is used to amplify specific regions of the DNA. This technique allows the production of numerous copies of the targeted DNA sequences.
  • Short Tandem Repeats (STR) Analysis: STR analysis is performed by examining specific regions of DNA called short tandem repeats. These regions consist of repeating DNA sequences that vary in length among individuals. The number of repeats at each STR locus is determined and used to create a DNA profile.
  • Electrophoresis: The amplified DNA fragments are separated by size using a technique called electrophoresis. The DNA fragments are placed in a gel matrix and subjected to an electric current, causing them to migrate through the gel. This process separates the DNA fragments based on their sizes.
  • DNA Profile Generation: The separated DNA fragments are visualized, and the resulting pattern is captured as an individual’s DNA profile. The DNA profile consists of a series of bands corresponding to the sizes of the amplified STR regions.
  • Comparison and Interpretation: The generated DNA profile is compared to known reference samples, such as those from suspects or victims. The comparison is used to determine if there is a match or exclusion. Statistical calculations, such as the random match probability (RMP), may be used to assess the significance of the match.

Role of DNA analysis in criminal investigations

  • Identification: DNA analysis is used to identify individuals involved in a crime. By comparing DNA profiles from crime scene samples to reference samples, such as those collected from suspects or victims, investigators can establish or exclude a person’s presence at the crime scene.
  • Linking Suspects to Crime Scenes: DNA evidence can be compared to a suspect’s DNA profile to determine if they were present at the crime scene. If a match is found, it provides strong evidence connecting the suspect to the crime.
  • Exclusion of Innocent Individuals: DNA analysis can be used to exclude individuals who are not connected to a crime. If a DNA profile from the crime scene does not match a suspect’s DNA, it can help establish their innocence.
  • Cold Case Investigations: DNA analysis has been instrumental in solving cold cases where conventional evidence has been limited. Revisiting old DNA samples or re-analyzing evidence using advanced techniques can lead to the identification of previously unknown suspects or the exoneration of wrongly convicted individuals.
  • Establishing Biological Relationships: DNA analysis is employed in cases involving missing persons, unidentified bodies, and disputed paternity or maternity claims. By comparing DNA profiles, investigators can determine familial relationships or confirm parentage.
  • Sexual Assault Cases: DNA analysis is particularly significant in sexual assault cases. DNA evidence collected from the crime scene, victim, or perpetrator can provide crucial information for identifying and convicting the offender.
  • Decoding Crime Scene Evidence: DNA analysis can help decipher complex crime scene evidence. By analyzing DNA profiles from different sources, such as mixed DNA samples, touch DNA, or degraded DNA, forensic experts can unravel critical information about the sequence of events and potential contributors.
  • Corroboration of Witness Testimony: DNA evidence can corroborate or challenge witness testimony. When witness accounts are in question, DNA analysis can provide objective evidence to support or refute their claims.

Critical Examination of DNA Reports

  • In recent judgments, such as Rahul v. State of Delhi, Ministry of Home Affairs (2022) and Manoj v. State of Madhya Pradesh (2022), the Supreme Court has raised concerns about the reliability and admissibility of DNA evidence in criminal cases.
  1. Rahul v. State of Delhi:
  • In Rahul v. State of Delhi, the Court expressed reservations about the reliability of DNA evidence based on the suspicion surrounding the collection and sealing of samples sent for examination.
  • Despite a match result and other findings, the Court acquitted all three individuals accused of rape and murder.
  1. Manoj v. State of Madhya Pradesh:
  • In Manoj v. State of Madhya Pradesh, the Court identified the likelihood of contamination in the DNA analysis due to the absence of mentioning the random occurrence ratio.
  • The Court emphasized the importance of considering the statistical ratio or ‘random match probability’ (RMP), which indicates the frequency of a particular DNA profile in a population. The lack of mention of RMP led to the exclusion of the DNA evidence in this case.

Concerns over the admissibility of DNA reports

  • Reliability of Techniques: The Court has questioned whether the techniques used in DNA analysis were reliably applied. It is crucial to ensure that the methods employed are scientifically sound and that the experts conducting the analysis possess the necessary expertise.
  • Examination of Underlying Findings: The Court has criticized the failure of trial courts and higher courts to examine the underlying basis of the findings in DNA reports. It is essential to scrutinize the methodology, procedures, and conclusions drawn from the analysis to determine the accuracy and reliability of the results.
  • Chain of Custody: The Court has expressed concerns about the integrity of DNA samples and their handling throughout the chain of custody. Proper documentation and maintenance of the chain of custody are vital to establish the authenticity and reliability of the evidence.
  • Possibility of Contamination: Contamination of DNA samples can significantly impact the reliability and accuracy of the analysis. The Court has highlighted instances where contamination may have occurred, such as improper collection, storage, or handling of samples.
  • Random Occurrence Ratio (RMP): The Court has emphasized the importance of including the random occurrence ratio or RMP in DNA reports.

Way ahead

  • Standardized Guidelines: Establish standardized guidelines for DNA analysis in forensic laboratories, including protocols for sample collection, handling, storage, and analysis. These guidelines should encompass best practices to minimize the risk of contamination and ensure the integrity of DNA evidence.
  • Quality Control Measures: Implement rigorous quality control measures in DNA analysis processes. This includes regular proficiency testing, accreditation of forensic laboratories, and adherence to international quality standards.
  • Chain of Custody: Emphasize the importance of maintaining a proper chain of custody for DNA samples. Accurate documentation and strict adherence to protocols will help ensure the integrity and admissibility of DNA evidence in court.
  • Research and Technological Advancements: Encourage research and development in the field of DNA analysis to further enhance the reliability and accuracy of techniques. Explore emerging technologies, methodologies, and advancements in forensic genetics that can improve the analysis of DNA evidence.
  • Expert Testimony: Enhance the understanding of DNA analysis among legal professionals, judges, and juries. Training programs and workshops can help educate stakeholders about the principles, limitations, and significance of DNA evidence. This will facilitate better comprehension and assessment of DNA reports during legal proceedings.
  • Collaboration and Peer Review: Foster collaboration among forensic laboratories, DNA experts, and legal professionals to promote knowledge sharing and peer review. This will help maintain high standards of DNA analysis and ensure continuous improvement in the field.


  • Despite recent concerns, DNA analysis continues to be a valuable tool in criminal cases. By addressing the raised issues through standardized guidelines, quality control, and improved understanding, the admissibility and reliability of DNA reports can be enhanced, contributing to a fair administration of justice.

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