In just a few decades, the science of DNA testing revolutionized criminal justice. The presence of a person’s DNA at a crime scene may be enough to secure a conviction.
According to Ryan Forensic, DNA testing systems, today are so sensitive that they can analyze extremely small samples. Also referred to as touch DNA, trace DNA refers to skin cells left behind from casual interactions with other people, either directly or indirectly. Trace DNA can contaminate crime scenes and lead to wrongful convictions.
How many cells can testing detect?
When a person touches an object or another person, he or she can leave up to 169 nanograms of DNA behind. This is more than enough for a testable sample at a crime scene, which requires only one or two nanograms at most. On an average day, a human being sheds approximately 400,000 cells or about 2,667 nanograms of DNA, most of it in increments so small as to be unnoticeable, such as flecks of skin shed while scratching an itch or minuscule drops of saliva while speaking.
How can trace DNA lead to criminal charges?
While testing can detect minimal amounts of trace DNA, it cannot differentiate where it came from. This deprives testers of the context needed to determine whether it came from criminal activity or an innocuous chance encounter. Another problem is that when one person has another person’s DNA on his or her body, the first person can unknowingly transfer it to other objects and even other people through normal day-to-day interactions, far away from the original source.
It is impossible to exercise control over one’s DNA, and in most cases, it is irrelevant because it does not have an impact on day-to-day life. However, if trace DNA appears at a crime scene, it could lead to false accusations of a crime.