If the prosecution intends to use DNA evidence to seek a conviction, it’s important you don’t give up hope. While this evidence can appear compelling and has helped prosecutors score numerous convictions, it is not infallible.
Defendants have still walked out of court as free men or women in cases where DNA evidence was used. Here are some of the reasons that can happen:
Someone else brought your DNA to the scene
DNA can travel far and wide. It’s known as secondary DNA transfer. One famous case involved a member of an ambulance crew attending to a drunken, homeless man and then attending a murder scene. Police found DNA belonging to the homeless man at the crime scene and arrested him on suspicion of murder. Yet he had never been there – the paramedic had unknowingly transferred some of the man’s DNA from one scene to the next.
The police or laboratory mixed up DNA samples
An officer attends an alleged crime scene and gathers evidence. Before they can return to the station to deposit the evidence, they are called to another crime scene where they collect more physical evidence. This could happen multiple times throughout the day. When they get back to the station at the end of their shift, they accidentally categorize one piece of evidence under the wrong file.
Or, if the police classify it correctly, the lab might mix two samples up. Both scenarios could lead to the prosecution alleging the police found your DNA somewhere they did not.
Learning more about the possible weaknesses of DNA evidence can help you determine what steps to take if you face criminal charges involving it.