3 ways DNA can become contaminated

In December 1999, an elderly woman was found dead in her home. According to Cleveland Magazine, a man was found guilty of assaulting and murdering her. He spent 11 years in prison before the verdict was overturned because law enforcement had manipulated an informant in order to arrest the man. Further, the DNA at the crime scene did not match the suspect. The true killer remains at large because that DNA evidence – a pubic hair – had been contaminated. Research shows that it was mixed with the DNA of a lab worker who had tested it.

As a sex crime lawyer in Minneapolis may have seen, there are several ways that DNA evidence may become compromised, such as the following:

  1. Improper collection method

As a report from the National Institute of Justice points out, how DNA is contaminated often begins with the way it is collected. Dirt, debris, and other particles can affect the sample. Investigators should always ensure that they use disposable tools when collecting samples. Other instruments or equipment should be cleaned thoroughly both before and after handling the evidence.

  1. Mixed with another source

Any sex crime lawyer in Minneapolis knows that DNA from a sample can become easily mixed with another strand of DNA. This can occur when the following happens:

  • Someone touches an area of a crime scene where DNA may be
  • Someone sneezes or coughs over the evidence
  • Someone fails to wear gloves when handling the evidence

The NIJ recommends that anyone handling samples of DNA should not only wear gloves, but they should change those gloves often. Many times, people may touch their face, nose, or mouth while working and then touch the sample, which can contaminate the evidence.

  1. During transportation and storage

Transporting and storing DNA evidence begs for proper techniques. The NIJ notes that all evidence should be air-dried and kept at room temperature to avoid destroying the DNA. Plastic bags should not be used, nor should staples. Studies show that plastic bags can retain moisture that will damage DNA evidence. Instead, investigators, forensic scientists, and others who handle the evidence should use new paper bags and envelopes.

After properly securing the samples, the NIJ suggests that they should be properly labeled so there is no confusion over what is inside the packaging. The evidence should then be stored in an area that will not get hot, as direct sunlight and heat can destroy or alter DNA.

Unfortunately, human error leaves plenty of room for DNA evidence collected at a crime scene to become contaminated. People charged with a crime should be aware that DNA samples are not always accurate. Anyone with questions regarding this matter should consult with a sex crime lawyer in Minneapolis.

Max Keller has won countless jury trial cases involving misdemeanors and felonies, sex crimes, and DWI’s. He is a member of the Minnesota Society for Criminal Justice, which only allows the top 50 criminal defense attorneys in the state as members. Max is a frequent speaker at CLE’s and is often asked for advice by other defense attorneys across Minnesota.

Years of Experience: Approx. 20 years
Minnesota Registration Status: Active
Bar & Court Admissions: State of Minnesota Minnesota State Court Minnesota Federal Court 8th Circuit Federal Court of Appeals State of Maryland

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