Is DNA Evidence Foolproof?

DNA evidence is arguably the most important development in forensic science of the last century. Law enforcement officers and criminal investigators have access to a wide array of scientifically backed evidence-gathering techniques to more accurately charge and convict offenders. While DNA evidence may seem inarguable in some cases, it’s vital to remember that DNA evidence is not a foolproof means of securing a conviction.

DNA evidence made its debut as evidence in an active trial in the 1980s, and since then has played a significant role in countless criminal proceedings. Most jurors and policymakers display strong faith in the accuracy of DNA evidence, but many factors can potentially compromise a piece of DNA evidence or render it less valuable to an active trial.


Many potential issues can arise when it comes to DNA evidence for a criminal trial. First, the investigators must find a large enough sample to conduct an accurate test. Common examples of DNA samples taken from crime scenes include blood, hair follicles, skin particles, and semen. If the investigators have a larger sample, DNA testing is easier to perform and will produce more accurate results.

It’s vital to remember that the technicians who handle and process DNA evidence do not map out a suspect’s entire genetic code. Instead, they refer to 13 loci, or unique identifiers, that help them narrow down the list of potential owners of the sample. A 14th loci helps technicians determine the gender of a sample’s owner. Most people will share about half of these loci with close blood relatives, and a few with complete strangers. The odds of sharing all 13 with another stranger are less than one in one trillion.


While this may sound like a surefire way to identify the owner of a DNA sample, this is not entirely true. A DNA sample present at a crime scene months before a crime takes place in that location may still become evidence, potentially leading to the questioning or arrest of an entirely innocent person completely unattached to the investigation. Time also influences the accuracy of DNA test results in other ways, as some environmental factors such as heat, humidity, sun exposure, and natural degradation with time will compromise the integrity of a DNA sample.

Sometimes a person’s DNA evidence on another person can cause complications with an investigation. For example, crime scene investigators in California discovered skin cells under the fingernails of a murder victim. This is common because some murderers will sustain wounds while subduing a victim. The victim will tear and scratch at the murderer defensively, sometimes scraping skin cells with their fingernails. In this case, the owner of the skin cells had a criminal record, so at first it appeared to be a slam-dunk investigation. However, that person was in the hospital at the time of the murder, and the skin cells found their way under the victim’s nails prior to the murder through another interaction.


It’s vital for anyone wrongfully accused of a crime to remember their rights. Even if the prosecution claims DNA evidence exists proving the accused is guilty, this is not always the case. Improperly obtained or stored evidence, mistakes by lab technicians, or contaminated test samples can all lead to false positives or even erroneous convictions. Many convictions in recent years have led to appeals and eventually overturned convictions due to the misapplication or mishandling of DNA evidence.

Anyone falsely accused of a crime and facing DNA evidence should immediately retain a reliable defense attorney. An accomplished defense attorney can help a wrongfully accused defendant clear his or her name by scrutinizing the manner in which the DNA evidence was gathered, handled, and processed.