Cases where the science involved is highly specialized and perhaps even esoteric, the central role of an expert cannot be disputed [Ramesh Chandra Agrawal v. Regency Hospital Limited, (2009) 9 SCC 709]. Be that as it may, it cannot be forgotten, opinion evidence is advisory in nature, and Courts are not bound by evidence of experts [Pali Ram, (1979) 2 SCC 158; Jai Lal, (1999) 7 SCC 280; Baso Prasad, (2006) 13 SCC 65]. Like all other opinion evidence, the probative value accorded to DNA evidence also varies from case to case, depending on facts and circumstances and the weight accorded to other evidence on record, whether contrary or corroborative. This is all the more important to remember, given that even though the accuracy of DNA evidence may be increasing with the advancement of science and technology with every passing day, thereby making it more and more reliable, we have not yet reached a juncture where it may be said to be infallible.

There cannot be any dispute that evidence on superimposition is also based on experts’ opinion. We would like to note, the use of the superimposition technique in investigations for identification purposes is not a new phenomenon. Notably, it has been employed in the investigations pertaining to the Nithari murders, the Russian murder incident in Goa in 2008, and even before that in the Morni Hill murder case and the Paharganj bomb blast case as far back as in 1996, and the Udhampur murder case in 2005. This Court itself has placed reliance on identification of the deceased through superimposition on several occasions [Shankar & Ors, (1994) 4 SCC 478; Swamy Shraddananda, (2007) 12 SCC 288; John David, (2011) 5 SCC 509; Mahesh Dhanaji Shinde, (2014) 4 SCC 292], clearly indicating that it is an acceptable piece of opinion evidence.

It is relevant to note, all of the decisions of this Court cited in the above paragraph were based on circumstantial evidence, involving aspects such as the last seen circumstance, motive, recovery of personal belongings of the deceased, and so on, and therefore in none of the cases was the superimposition technique the sole incriminating factor relied upon to reach a conclusion of guilt of the accused. Indeed, in Mahesh Dhanaji Shinde, Court also had the advantage of referring to a DNA test, and in John David, of referring to a DNA test as well as dental examination of the deceased, to determine the identity of the victim. This is in line with the settled practice of Courts, which generally do not rely upon opinion evidence as the sole incriminating circumstance, given its fallibility. This is particularly true for the superimposition technique, which cannot be regarded as infallible.

– Hon’ble Justice Mohan M. Shantanagoudar, Pattu Rajan v. State of Tamil Nadu, [Criminal Appeal Nos. 680-681 of 2009].

Also see, Kaleeswaran v. State, [Criminal Appeal No. 160 of 2017] decided on 03.11.2022.