Contamination may pose hurdles during DNA tests
NEW DELHI: The extraction of DNA samples from the body parts allegedly disposed of in a drain by the suspect in the Shraddha Walkar case may prove to be tricky since the human remains may have been contaminated by the sludge and toxic elements in the drain water, said experts from the Delhi Forensic Science Laboratory (FSL).
The Delhi Police have recovered at least 13 pieces of bones at the instance of Aaftab Amin Poonawala who allegedly murdered and chopped Walkar’s body and disposed of the parts at several locations in south Delhi.
FSL officials said that the police were yet to hand over the samples to them. The officials added that after the recovered samples are shared with the laboratory, they will be cleaned and the procedure to isolate the bone marrow and extraction of DNA samples will begin. Explaining the process of DNA profiling, FSL assistant director Sanjeev Kumar Gupta said that the analysis is done in four stages, beginning with the extraction of DNA from the collected samples such as bones, blood, hair, nails, etc. “DNA is found inside the nucleus of a cell. So, it is extracted with the help of phenol chloroform method and preserved in a buffer. The second stage is DNA quantification that is done to check the quality and quantity of the DNA. The third stage is called PCR amplification. As the DNA is in small quantities from forensic samples, it is amplified by polymerase chain reaction(pcr) and billions of copies are produced. The final stage is DNA sequencing wherein DNA sequences are produced in the form of peaks in a graph and matched with the standard samples,” Gupta said.
On Saturday around 11 am, a two-member FSL team visited the forested area where personnel from the Mehrauli police station were present along with Poonawala. The policemen told the forensic experts that some bones were seen in a drain. The forensic experts collected the pieces of bones, stored in boxes and handed over to the police.
They also visited the flat, where Poonawala allegedly confessed to have strangled Walkar, chopped her body into at least 35 pieces.
Poonawala accompanied the police and forensic personnel to the flat and showed the bedroom where he allegedly strangled Walkar, and the bathroom where he chopped her body. He told the personnel that he had cleaned the flat several times using “hypochlorous acid” and other toilet and floor cleaning solutions. “We carried out the benzidine test in the flat and the fridge to find traces of blood. While the bathroom and the refrigerator were found clean, some traces of blood were found on the platform and wooden cabinets of the kitchen sink. We will analyse the sample to ascertain if they belong to Walkar or Poonawala,” said another forensic expert.
Retired Delhi police officer Maxwell Pereira said that forensic experts have the ability to extract DNA samples from “even 100 years old remains”. “If the recovered parts are indeed of the same woman, then it can be easily analysed,” said Pereira who supervised the probe in the 1995 Delhi Tandoor murder case.