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How can trace DNA evidence lead to a wrongful conviction?

A loose eyelash, a chipped nail, saliva or fingerprints — just about everywhere you go you leave some kind of DNA evidence behind. For decades, tracing DNA evidence back to someone was nearly impossible — a fictional dream that any criminal investigator would wish for. Now, technology has evolved so much in the last 30 years that even a stray hair could be linked back to its origins.

Typically, people aren’t bothered by what DNA they leave around, but even a single shred of skin could link a person to a criminal investigation. Here’s what you should know:

How much DNA is needed to trace it?

With today’s technology, even a small sample of DNA may be traceable. A stray hair or dandruff can contain a lot of DNA evidence, but even touching an object could leave behind a trace of a person’s presence.

It’s believed that people leave behind upwards of 169 nanograms of DNA evidence when they touch something — that’s out of the 400,000 cells people shed every day. Out of those 169 nanograms of DNA evidence, only 2 nanograms (or 300 cells) may be needed to trace someone’s DNA. In other words, DNA analysts may only need a fraction of the original DNA sample to trace it to an individual.

When DNA evidence is misleading: Wrong place, wrong time

Forensic DNA specialists may be able to identify who the DNA is from, but in a criminal case, DNA evidence has one major flaw: DNA analysis can’t explain why evidence is present at a crime scene. Because of this, there is the real possibility that a suspect whose DNA was found at a crime scene could be wrongly convicted of a crime — just because that person was at the wrong place at the wrong time. A person may even become a suspect in a criminal investigation just by brushing up against someone else earlier in the day. Even scratching an itch at a friend’s house could leave behind enough evidence to spark an investigation of the person who had an itch.

Furthermore, DNA evidence may be transferred from a primary contact to a secondary or even a third contact. What this means is that a person may have never touched an object directly, but that person’s DNA was transferred through multiple contacts to the object. For example, a pen, envelope or cup may have been handled by multiple people, resulting in someone’s DNA being transported into an investigation scene.

No matter what you do, you’ll likely still leave DNA evidence everywhere you go. Your DNA may even be transferred to places you’ve never been. Whatever your situation may be, if you are being investigated or facing a criminal charge, it is never too early to seek legal counsel and representation.

For more on that, please see our overview of what to look for when choosing a criminal defense attorney.