Infallibility of DNA Evidence Challenged By Shiavngi Gupta from Amity Law School, Delhi
“DNA results can be in the eye of the beholder”
In the world of a criminal lawyer the trail to conviction can be a long and arduous one. When criminals strike, they do their best to make sure that every T is crossed and all the I’s are dotted. Investigators would sift through a tangle of evidence at the crime scenes to come up empty handed or without any substantial evidence. That is until a scientific breakthrough in 1984 shook the world of forensic science - DNA fingerprinting; powerful evidence with firm roots in science and backed by statistics. It was touted as an unassailable technique to prove guilt, identify the victim or overturn wrongful convictions by the law enforcement community. And for a time, it was.
When British geneticist Sir Alec Jeffreys accidentally discovered DNA Fingerprinting, he assisted the police in solving two murder mysteries. In both the cases, Jefferys compared a large sample of DNA found at the crime scene to another large sample of DNA from the suspect. All humans have 99.9 percent of their genes in common. That is what makes us all homo sapiens. It's that last 0.1 percent that differs and that geneticists look for during DNA analysis. There are certain pairs of genes (a.k.a alleles) that vary from one person to another. Typically, these alleles are compared at 13 specific locations in the DNA chain. The probability of two different people matching at all 13 locations is less than one in a billion, thus, making Jeffreys’ technique highly accurate.
With the advancement of science, the scientists developed the technique to use smaller samples. Because DNA double helix is contained in every cell, every piece of a person's body, even the tiniest skin follicle may be used to identify a person using DNA fingerprinting. This makes it more serviceable for law enforcement machinery to identify the criminal as it is virtually impossible to remove all physical traces of one's presence from the crime scene. Just a trace of blood, a strand of hair or an imprint of lipstick on a glass is enough to reach a conclusive finding.
And this is where the problem began!
The reliability of DNA evidence depends on a myriad of factors such as the quantity and quality of the sample. The crime sites do not provide the sterile conditions of a laboratory and the chances of DNA contamination are high. And contaminated DNA means imprecise results.
Biologist Greg Hampikian’s team collected five soda cans from an office after lunch and put them in individual evidence bags. Then, without changing gloves, they put five newly bought knives into separate evidence bags as well. Hampikian’s group looked for the DNA in the miniscule sample available and found DNA from a member of the staff on one of the knife blades who had not touched or even been in the same room with the knives.[i]
If the DNA sample collected from the crime scene is a mixture, the uncertainty is magnified. It is to be decided how many people's DNA are involved, which alleles belong to which person and whether any alleles have disappeared. This leaves room for interpretation, making the findings of such DNA analysis subjective; and wherever there is subjectivity; there is room for doubt and human errors.
This has been confirmed by geneticist Michael Coble of the National Institute of Standards and Technology in Gaithersburg, Maryland. His team set up a scenario in which a mix of DNA from several people had been found on a ski mask. 108 labs were asked to determine whether a separate DNA sample was also part of the mix. Seventy-three of the labs incorrectly determined that the separate DNA was a part of the mix. The study shook the confidence that the community had in DNA evidence.[ii]
As the technique of DNA Fingerprinting has gained popularity, its accuracy has diminished. Today it is not the irrefutable proof that the courtrooms and general public believe it to be. All over the world, there are innumerable cases where innocent people have had to pay the price for this scientific fallacy. However, this does not mean that the technique has lost all of its credibility. If proper precautions are taken, in competent hands, DNA analysis can provide conclusive evidence; but in less than ideal situations, the technique is not without its own flaws which cannot be overlooked by the justice administration system.
[i]Worth, Katie. “The Surprisingly Imperfect Science of DNA Testing.” Frontline and The Marshall Project. Web.
[ii] Star, D. (2017, July 26). Forensics gone wrong: When DNA snares the innocent. Retrieved from http://www.sciencemag.org/news/2016/03/forensics-gone-wrong-when-dna-snares-innocent
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