Touch DNA test would not have helped in Aarushi case: ExpertBy Anjali Ojha, IANS
Thursday, December 30, 2010
NEW DELHI - Murdered teenager Aarushi Talwar’s parents feel that a touch DNA test may have helped nail her murderer but experts from Hyderabad-based Centre for DNA Fingerprinting and Diagnostics (CDFD) say the test does not yield reliable and “robust evidence”.
Touch DNA test analyses skin cells left behind when an assailant touches a victim or objects at the crime scene.
Experts say the chances of contamination of a sample are very high in a touch DNA test, which brings down its reliability.
“The touch DNA test is not considered a very robust evidence anywhere in the world as chances of contamination of a sample are very high,” J. Nagaraju, director in-charge and molecular genetics scientist at the CDFD, told IANS.
The CDFD, an autonomous body under the ministry of science and technology, conducted DNA and forensic tests in the Aarushi murder case when the Central Bureau of Investigation (CBI) took over the probe from Uttar Pradesh Police.
As the central investigating agency Wednesday announced it was filing a closure report in the trial court, Aarushi’s parents said that a touch DNA test could have solved the case.
“I had researched a lot about touch DNA test and asked the CBI more than a year-and-half ago to get it done. But they did not. The test could have revealed who was there in the room on the night of Aarushi’s murder,” Aarushi’s father Rajesh Talwar told reporters Thursday.
Aarushi, the daughter of dentist parents Rajesh and Nupur Talwar, was found murdered mysteriously in their Jalvayu Vihar apartment in Delhi’s suburban Noida May 16, 2008. The family’s domestic help, Hemraj, whom Noida police initially suspected for the murder, was also found killed a day later on their flat’s terrace.
Aarushi’s father was arrested and kept behind bars for 50 days in connection with the two killings, but he was later let off because of lack of evidence against him.
According to Nagaraju, the touch DNA test was not the best option for solving the Aarushi case.
“In touch DNA analysis, the DNA is amplified from a small sample which is left from the human body on objects on the crime scene. From the small sample, the DNA is amplified and a profile is prepared,” Nagaraju said.
Unlike the normal DNA test which takes a larger sample of cells, the touch DNA test requires only seven or eight cells from the outermost layer of skin.
“Though the technique is simple, the method of collecting sample is critical. The chances of contamination are high,” he said.
“If someone else has touched the object (from which skin cells are lifted), their DNA will also be amplified and it will be difficult to zero in on the criminal. So it is not a very robust method of getting evidence,” he said.
The scientist said because of these complications attached to the test, it would not have proved a good method for finding evidence in Aarushi case.
“This case was transferred from one agency to the other, so it was difficult to get any conclusion based on this test,” he said.
CDFD director J. Gowrishankar had earlier expressed difficulty in collecting evidence through various conventional tests - other than touch DNA - conducted on objects found on the crime scene.
“The CBI had asked us to inspect various articles that were found in the flat. None of them gave any evidence to link the suspect, whom the CBI had in their mind, to the crime,” Gowrishankar said Wednesday.
Nagaraju added that the touch DNA test could be challenged in court.
“Even the DNA samples of police officers who might have touched objects at the crime scene may get recorded in touch DNA test. In many foreign countries, it is not used as a conclusive evidence,” he said.
The CDFD is the only agency in India which conducts the touch DNA test, primarily because of the complications related to sample collection and the need for a sophisticated laboratory.
(Anjali Ojha can be contacted at firstname.lastname@example.org)