How a DNA test can nail Aftab in Shraddha murder case?

Since polygraph and narco test results are inadmissible in court and Aftab did not reveal anything new in these tests, a DNA match becomes very crucial for the police to nail Aftab.

New Delhi, Dec 06: In the gruesome murder case of 27-year-old Shraddha Walkar, the Delhi Police are collecting all the evidence against accused Aftab Amin Poonawala and a DNA match of the recovered body parts in the Mehrauli forest with that of Shraddha's father and brother is crucial. This match can be a determining factor in earning a conviction in a court of law.

The Delhi Police is yet to receive the DNA analysis test report from Central Forensic Science Laboratory (CFSL), and in case the DNA samples don't match, the police will have to rely on circumstantial evidence to prove their case against Aftab as the polygraph and narco test results are inadmissible in the court of law.

Let us now have a closer look on how does DNA testing work? What major cases have been cracked because of it.

What is a DNA?

DNA, known as deoxyribonucleic acid, is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses. The human genome contains 3.2 billion nucleotide base pairs (A, T, G and C). It is highly conserved between people, with every human sharing close to 99.9% of his genome with the rest of the population. For example, the DNA in a man's blood is the same as the DNA in his skin cells, semen, and saliva.

DNA fingerprinting has helped solve many cases around the world, freed the innocent and revolutionised science and criminal justice. The technique was first developed on 10 September 1984 by geneticist Alec Jeffreys in the UK.

According to National Criminal Justice Reference Service (NCJRS) website, DNA is a powerful tool because each person's DNA is different from every other individual's, except for identical twins. DNA collected from a crime scene can either link a suspect to the evidence or eliminate a suspect, similar to the use of fingerprints. It also can identify a victim through DNA from relatives, even when no body can be found. And when evidence from one crime scene is compared with evidence from another, those crime scenes can be linked to the same perpetrator locally, statewide, and across the nation.

How DNA testing is performed?

DNA can be left on clothing, tools, weapons, underclothes, masks, hats, gloves, bedding, dirty laundry, fingernail scrapings, cigarette butts, toothpicks, toothbrush, Condoms, Stamps or envelopes, Cups/bottles, Sexual assault evidence kits, facial tissue, hairbrush, eyeglasses, ligatures (rope, wire, cords).

Most DNA samples submitted to a laboratory undergo the following process:

• Extraction is the process of releasing the DNA from the cell.
• Quantitation is the process of determining how much DNA you have.
• Amplification is the process of producing multiple copies of the DNA in order to characterize it.
• Separation is the process of separating amplified DNA product to permit subsequent identification.
• Analysis & Interpretation is the process of quantitatively and qualitatively comparing DNA evidence samples to known DNA profiles.
• Quality Assurance is the process of reviewing analyst reports for technical accuracy.

Factors that can affect DNA

Forensically valuable DNA can be found on evidence that is decades old. However, several factors can affect the DNA left at a crime scene, including environmental factors (e.g., heat, sunlight, moisture, bacteria, and mold). Therefore, not all DNA evidence will result in a usable DNA profile. Further, just like fingerprints, DNA testing cannot tell officers when the suspect was at the crime scene or for how long, according to NCJRS.

Where is DNA contained in the human body?

The biological material used to determine a DNA profile include blood, semen, saliva, mucus, perspiration, fingernails, urine, feces, hair, teeth, bone, tissue and skin cells.

Cracking cases

Several high profile assassination cases in India have been cracked by using DNA, such as that of former prime minister Rajiv Gandhi and former Punjab chief minister Beant Singh, the murder of Naina Sahni, Sheena Bora murder case, the paternity case of former Union minister ND Tiwari, the Priyadarshini Mattoo case, the Delhi bus gangrape case, the Hyderabad blasts case and to convict Bollywood actor Shiney Ahuja.

In Shraddha Walkar's case, police have to test the bloodstains found in Aftab's kitchen as well as compare the bones found in the Mehrauli forest to the blood samples given by her father Vikas Walker and brother.