Thanks to true-crime television shows and forensic dramas, the American public is largely familiar with the use of DNA evidence in criminal cases.
What they don’t necessarily know, however, is that DNA evidence isn’t actually the “cincher” in a criminal case. In fact, the best use of DNA evidence may be ruling out someone’s involvement in a crime — not proof of guilt.
Consider this: Human beings shed thousands of tiny skin cells every single day. In fact, household dust is largely comprised of dead skin cells. You probably leave skin cells behind you wherever you go — and those skin cells get picked up and transferred around by other people all the time. That means that your genetic material can end up passed along to places that you’ve never even been — and some of those places can end up being crime scenes.
For example, imagine that you black out somewhere and wind up in an ambulance. You naturally leave plenty of skin cells behind in the ambulance. Some of those skin cells end up on the clothes of the paramedics who treated you. Later that evening, the paramedics get called to the home of a murder victim. Your DNA, in the form of skin cells too small to be noticed by the naked eye, ends up transferred from the clothing of one of the paramedics to the victim’s body — where it is eventually collected by technicians and tested. Suddenly, your DNA is linked to a murder — even though you were miles away at the time.
This isn’t a far-fetched scenario, either. It actually happened to someone. And this isn’t the only problem with DNA evidence.
A single sloppy technician could easily contaminate a whole lab full of genetic samples — leading to incorrect test results. There’s also no way to tell for sure when DNA is left behind — so your skin cells could potentially be sitting around in someone’s home after you visited for months (depending on how often they clean). If that person ends up the victim of a crime, you could be wrongfully accused.
These are just a few of the reasons that defendants should not give up hope of an acquittal when the prosecution says it has DNA evidence. An experienced criminal defense attorney can help the jury understand that DNA is actually quite fallible.