Advances in forensic DNA analysis have made it much easier to definitively tie defendants to a crime through biological evidence, and that can make juries more confident about their verdicts when they vote for a conviction. But, should juries really be that comfortable relying on DNA? What if the DNA analysis gets things wrong?
While DNA evidence is typically treated as absolute proof of someone’s presence at a crime scene, the ability of forensic tests to pick up on very tiny amounts of someone’s genetic material actually presents some unique challenges and risks. So-called “trace DNA” can actually travel quite far from its host.
A near-miss illustrates the problem
To see how dangerous reliance on trace DNA evidence can be, you have only to look at a Silicon Valley case from 2012. A homeless man was facing a potential death sentence after trace DNA placed him at the scene of a brutal murder inside a millionaire’s home.
The only thing that saved him was the fact that he’d been under constant supervision in a hospital some miles away at the time of the murder. Investigators discovered that the paramedics who responded to the murder scene were the same ones that had transported the homeless man to the hospital earlier – and they carried his DNA with him on their clothing or equipment later.
This incident illustrates one of the primary concerns with trace DNA evidence, which is the potential for contamination and transfer. Due to its small quantity, trace DNA is incredibly susceptible to contamination from external sources. Even a momentary touch or indirect contact with an item can transfer DNA. Contamination can occur during crime scene collection, evidence processing or even in the laboratory.
Modern DNA testing techniques have become increasingly sensitive, capable of detecting DNA at extremely low levels. While this sensitivity is advantageous in some cases, it also raises concerns. The more sensitive the analysis, the higher the likelihood of detecting DNA from sources unrelated to the crime. The presence of an innocent person’s DNA at a crime scene does not necessarily mean they were involved in the offense, but it can significantly impact perceptions and interpretations.
While DNA can create a perception of guilt, especially when presented as conclusive evidence without considering alternative explanations, seeking experienced legal guidance can help you understand avenues for defense or a potentially successful appeal.