Thanks, perhaps, to the number of crime dramas we now consume as entertainment, the layman now believes that DNA evidence in a case is clinching – it can make or break a case. But unclouded by what we see on our screen, what is the truth about the probative value of DNA in establishing guilt or innocence?
In mid-June, the Madras High Court acquitted the rape accused in the POCSO case. In the bench of Justices MS Ramesh and Sunder Mohan J. found merit in the appeal by the man, who argued that although it was later proved that the victim falsely accused him of raping her, the DNA test to establish paternity has been a matter of blow, leading. to the belief. The judges considered that the prosecution did not prove the case against the petitioner beyond reasonable doubt, and therefore, imposed the sentence.
But it’s not all judgments are also examined, in detail, the policy relies on DNA evidence only to establish guilt. The facts of the case are as follows: The victim originally stated that the plaintiff had committed a penetrative sexual attack on her, but, in her deposition, she said she had blamed the plaintiff, because she did not want a love relationship with another person to come. to the open because of fear of criticism from relatives. Prosecution witness 1 is also an enemy, and in that situation, it will not be possible to give a finding of guilt to the plaintiff, his lawyer argued in court. Thus, the conviction was based on a DNA report, which compared blood samples collected from her and the victim’s child. The report states that the cumulative probability of paternity of the petitioner as the father of the child (victim) is 99.999999998%.
How does DNA work?
DNA is deoxyribonucleic acid, and is the genetic material found in the nucleus of cells in living organisms. Judge Mohan and Ramesh relied on an article published by the Central Forensic Science Laboratory, Kolkata, explaining it in detail. The average human body is made up of about 100 trillion cells. DNA exists in the cell nucleus as a double helix, supercoiled to form chromosomes together with intercalated proteins. Twenty-three pairs of chromosomes are present in each cell nucleus, and a person is given 23 chromosomes from the mother and 23 from the father, which are transmitted through the ovum and sperm. All information about the internal organization, physical characteristics, and physiological functions of the body is encoded in the DNA molecule in the base (sequence) of the alphabet of four nucleotides or bases: Adenine (A), Guanine (G), Thymine (T), and Cytosine (C), together with a sugar phosphate backbone.
Since the same DNA sequence is present in every cell of the body (except for adult red blood cells); therefore, DNA can be sourced from any biological material. These include saliva, semen, vaginal fluids, blood, body tissues, teeth, hair, and bones. The amount of DNA present in biological material varies. Blood and saliva are richer sources of DNA compared to teeth and hair roots, which lack DNA. DNA can be left on objects during physical contact, commonly referred to as touch DNA or trace DNA. Touch DNA contains a very low amount of DNA and is not an ideal source for DNA profiling, explains the paper Indian Forensic Science Report (2013-2017), who studied the science behind forensic DNA profiling and its value in criminal proceedings, mainly acknowledged that there are limitations inherent in the process.
There is much to be said for the collection, packaging, storage, and transportation of DNA samples. Although it varies based on the source of the biological material and the conditions in which it is found, the idea is to ensure that the quality and quantity of DNA can be preserved. There are well-defined techniques for the collection and transport of different types of samples to prevent contamination and ensure the quality of the extracted samples.
How reliable is DNA?
But the moot question is: how reliable is DNA profiling in criminology? A basic fact to know is that the DNA in all humans is 99.9% identical. In forensic DNA profiling, several locations in the remaining 0.1% of DNA are selected to create a person’s DNA profile. The specific location where the DNA is examined is called a locus. This locus has repeated DNA sequences called Short Tandem Repeats, or STRs. While every individual has the same sequence, or STR, at a locus, the number of repeats can vary from individual to individual. Variations in the number of these repeats are called alleles. At a given locus, an individual has two alleles, one inherited from the father and the other from the mother. The current genetic marker of choice for forensic purposes is STR. STRs on the Y chromosome are used in cases of sexual assault or to determine paternal lineage.
DNA profiling is complex, and each sequential step to generate a profile can vary depending on the facilities available in the laboratory. However, the principles of analysis remain: isolation, purification and quantity of DNA, amplification of selected genetic markers, description of fragments and genotypes, statistical analysis and interpretation, the explanation of the Kolkata laboratory adds.
Head of forensic medicine and toxicology Manikanda Raj at Chengalpattu Medical College and Hospital, said DNA is a process based on probability and, in that sense, cannot be considered conclusive evidence. There are certain pitfalls, he said, especially with sample contamination, where there is a delay in picking up a sample or testing it, when the sample becomes unusable, or the sample itself is altered. “Then the test becomes uncertain. One way to ensure that at least the correct sample is tested is to videograph the entire process – something we have done in Tamil Nadu – thanks to the directive by Justice PN Prakash. He was very clear that conviction cannot be achieved only by strength of DNA analysis, without other evidence.
The Madras High Court, in its judgment in the case. also explains possible results, based on scientific resources. There are three results from profile comparison: (1) Match: If the DNA profile obtained from the two samples cannot be distinguished, it is said to match. (2) Exclusion : If the profile comparison shows a difference, it can only be explained by two samples coming from different sources. (3) Inconclusive : The data do not support a conclusion about the three possible outcomes.
It also quoted the Law Commission of India’s report, ‘Review of Indian Evidence Act, 2003’, which stated: “If a sample matches, it does not mean that the identity is fully proved. However, an expert will be able to deduce from the DNA sample database an approximate number of shows how often the same DNA “profile” or “fingerprint” is found. Maybe, for example, a matching profile is found in 1 person out of 1,00,000: This is described as a “random occurrence ratio”. investigation but not to raise suspicion of identity in court.
In Pattu Rajan v. State of TN 2019, the judge considers the value to be attached to the DNA report: “Like all other opinion evidence, the probative value given to DNA evidence also varies from case to case, depending on the facts and circumstances and the weight given to other evidence which is recorded, whether it contradicts or supports it. This is more important to remember, because although the accuracy of DNA evidence can be increased every day, thus becoming more reliable, we have not reached the point where it can be called impossible. Thus , it cannot be said that the absence of DNA evidence will lead to an adverse inference against a party, especially if there is other evidence that is reliable and trustworthy for that party.