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Monday, December 18, 2017 MAGAZINE Volume 1, Issue 1

Just How Infallible is DNA in Crime Scene Investigations?


by Julie Bowen

November 22, 2013

DNA is considered to represent the present and future of high tech, reliable forensic investigations at crime scenes, and its impressive results have been applauded throughout the criminal investigations sector, but lately we are seeing that DNA is not infallible. Contamination can occur, with misleading results and this can be frustrating for investigators, leading to wrongful arrests. The issue of contamination can be eradicated with common sense but with Touch DNA fast becoming a popular tool at the crime scene, we must realize its limitations and have an awareness of factors that can affect results.

Transference of DNA

The New York Times explored the issue of transference of DNA from one scene to another, which led investigators to the wrong suspect in the robbery and murder case relating to millionaire Raveesh Kumra last November. When a team of forensics visited the crime scene and found DNA on the victim’s fingernails, they traced this to another man and arrested him. The suspect, a Mr Anderson, had an airtight alibi however; he had spent that night in the Santa Clara Valley Medical Center in San Jose, heavily intoxicated. When his hospital records were produced, prosecutors could not put him at the scene of the crime, yet they could not see how to eradicate him either.

After spending 5 months in prison, facing a possible death sentence, Mr Anderson was finally released. Prosecutors in the case believe that transference of DNA had occurred when the same paramedics who transported Mr Anderson to the hospital responded to the call at the Kumra mansion the same night. Transference had most likely happened with DNA on the paramedics’ clothing or on their equipment.

DNA contamination was responsible for Amanda Knox’s appeal trial and is now at the heart of the re-trial in Italy. With the standards of collecting evidence falling below what was considered acceptable at a crime scene, the case hinged on DNA contamination, particularly on the murder weapon itself. There were low amounts of DNA at the scene, making it difficult to test genetic profiles with any degree of confidence. A court-appointed expert at the appeal trial had claimed that the data was very mixed and that the victim’s profile was the only one there that could be announced with any certainty.

So are we placing too much faith in DNA? And what can we do to eradicate the risks of contamination?

Touch DNA and Common Sense

When we consider that every contact leaves a trace at the crime scene, the science of DNA has evolved tremendously from the early days of evidence gathering. Profiles can now be gathered when there seem to be no bloodstains or body fluids at the scene, with the advent of touch DNA.

It is believed the scientists can retrieve a DNA profile from a mere five or six cells. Touch DNA is proving vital in violent crime cases where no fluids are being submitted for testing, but leads can still be made from this technology if a suspect has touched a surface or object at the scene or through the shedding of cells that occurs naturally and if they perspire, more cells are left behind. Touch DNA can, however, be contaminated.

There are simple rules to try to eliminate this, to avoid misleading information being processed by crime teams. Limiting access to the scene and to evidence is an obvious rule, but as we have seen in the Amanda Knox trial, the murder weapon itself was contaminated. Evidence should not be talked over and masks and PPE should be worn. Gloves should be frequently changed and fingerprint brushes need to be disposable. Samples to eliminate innocent bystanders and workers who have been in contact with the scene should be taken.

Domestic Violence and DNA

In cases of domestic violence, and particularly in stalking instances, DNA evidence can have a tremendous impact on the outcome. This evidence is now playing a major role in convicting or acquitting individuals, as scientists develop exciting new methods of extracting it and minimizing the risk of contamination. New studies are also being conducted that explore the effects of domestic violence on DNA and how DNA can be altered by other factors such as children’s exposure to their parent’s violence. Children ‘can be harmed by witnessing violence’, according Licensed Prescriptions, and now this fascinating study of DNA shows how it not only defines us but how it can be affected by violent situations in the home, even if we are not the physical victims ourselves. It was found that if children see or hear violence between their parents, the telomeres in their own bodies, which are DNA sequences, allow unraveling to occur, meaning that the child’s cells begin to die.

DNA has advanced criminal investigations considerably over the years. With careful execution, crime scenes should not be contaminated and touch DNA, as well as other DNA profiling should be able to do their jobs effectively. Human error causes contamination and transference and only when this is eradicated, will DNA become truly fallible.

Julie Bowen is a freelance writer who writes on a wide variety of topics.