Shraddha Walkar Murder: Why take time for DNA analysis of samples Challenging?

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DNA analysis from bone remains, how it's done and why it takes time

With the body parts recovered by Delhi Police in the Shraddha Walkar murder case being sent for DNA analysis for identification, forensic experts say the standard operating procedure for DNA sampling through bones is time-consuming.

"DNA analysis requires three major steps: Extraction of DNA from the sample, amplification of the extracted DNA, and analysis of that amplified DNA," says Dr. Tayyaba Tanvir, resident Doctor of forensic medicine at Delhi's Maulana Azad Medical College. DNA analysis from bone remains takes a lot of time, even with the best of technology, Dr. Tanvir adds.

Walkar was allegedly killed by her live-in partner Aaftab Poonawala, who later chopped her body and scattered the pieces in the Mehrauli forest. The police this week have recovered over 10 suspected body parts, mostly in the form of bones, and these need to be verified through forensic analysis. 

In samples like bones or teeth, the first step, i.e., extraction, takes a lot of time as the bone has to be pre-treated which involves decontaminating the bones from any foreign DNA sample, followed by pulverizing the bone to obtain DNA, Dr. Tanvir explains. This procedure alone can take more than a week, depending on the bone's type, structure, build, and thickness. 

Various methods can be used to perform the second and third steps, says Dr. Tanvir, adding that the method used depends upon the laboratory where the procedure is carried out. In simple, straightforward cases, it takes at least a week. "Once the DNA from the victim's sample is obtained, this DNA sequence is matched with her relatives' DNA to confirm the identity of the victim," she adds. 

In the case of Walkar, since the bones have been recovered from a forested area, there are chances that they could be misplaced or touched by animals. A senior official from the Forensic Science Laboratory, Rohini, had said the DNA analysis in the Walkar case could take two weeks as the samples were very old.

Dr. Pankaj Shrivastav, in charge of the biology division regional forensic laboratory at Bhopal, points out that though there can be a mix of animal bones and human bones, the testing kits are human-specific. "So, only human DNA will give a profile. Paternity of the missing person can be established by matching this profile with parents," Dr. Shrivastav adds.