Thanks to modern science (and, no doubt, a lot of exposure in television and movies) genetic evidence in the form of DNA has pretty much become the “gold standard” for proving someone’s guilt or innocence when there’s a violent crime.
But DNA isn’t infallible. While powerful, there are problems with the idea that the science of DNA is irrefutable.
What are the inherent problems with DNA evidence?
DNA can be collected from biological samples such as blood, saliva, hair and skin cells left behind at a crime scene – and increasingly smaller quantities are now being used to create profiles that can be presented in court to point to a given defendant.
While DNA evidence has probative value, it is not always reliable. Problems include:
- Contamination: There have been numerous incidents where DNA evidence has become contaminated, either at the crime scene during collection or in the lab where the samples were tested and the profiles created.
- Degradation: Biological samples can degrade over time, especially when exposed to environmental factors like heat, sunlight and moisture. Improper storage can lead to incomplete or false results.
- Human error: The science of DNA still requires human interpretation, and humans are inherently prone to biases and errors. Mistakes in collection, labeling or analysis can compromise the integrity of the evidence.
- Familial connections: DNA from twins will yield identical results, and DNA from close relatives can yield similar results. When samples are small, degraded or incomplete, mistakes are possible.
Finally, DNA can never tell you when someone was at a crime scene – or even if they were ever there. Genetic material can transfer from one person or object to another, and hang around for a long time. If you were in a store a week ago and the shopkeeper was murdered today, your DNA could still appear on their work apron just because they hadn’t washed it.
If you’ve been accused of a violent crime, and the police or the prosecutor tells you that your conviction is a “sure thing” because there’s DNA evidence against you, don’t believe them. There are more ways to attack DNA evidence than you likely know. An experienced defense is key.
