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Why should people be more skeptical of DNA evidence?

On Behalf of | Nov 18, 2019 | Sex Crimes |

How do you prove that someone is guilty of a crime? In the United States, you need to show juries enough evidence to convince them of a person’s guilt beyond all reasonable doubt. But what is reasonable?

Most people–and most jurists–are not scientists. They may be taught the basics of the scientific method in high school, but they tend to look at matters in relatively simple terms of cause and effect. They don’t always question the processes and probabilities that drive science. And that’s a disconnect that can have serious consequences, especially when these people serve as jurors in cases that rely on DNA evidence.

The mixed bag of DNA evidence

With the rise of commercial DNA testing, the police have increasingly turned to online genealogy sites for potential DNA matches. There are issues regarding the privacy rights involved, but there are also issues with the science. A recent article in Scientific American found that different ancestry tests often lead to different results, and it explored some of the reasons.

But while getting mixed results from your ancestry tests may be disappointing, it’s far worse to be convicted because of bad DNA testing. What are some of the ways DNA testing can fail? They include:

  • Faulty interpretations. In 2016, The Atlantic Monthly looked at the use of DNA evidence and pointed to a case where a man was jailed for rape based on a co-defendant’s testimony. The man expected his DNA test to show he wasn’t guilty, but the testers said his DNA could have matched the semen they tested. A pair of professors took interest in the case and sent the man’s DNA for testing. Of the 17 labs to which they sent it, 16 said the man’s DNA wasn’t a match.
  • Procedural errors. There are plenty of stories about labs that have tested the wrong samples, and they don’t always catch their mistakes. In fact, Scientific American noted that in one case, a commercial DNA sequencer mistook dog DNA for that of a human.
  • Jurors’ limited understanding. Due in part to the popularity of shows like CSI, the public believes that DNA testing is more accurate than it is. An Australian researcher found that sexual assault cases were two times more likely to go to trial if they involved DNA evidence and 33 times more likely to result in a guilty verdict.

DNA testing as part of the whole picture

Because DNA tests can fail, juries need to remember the context created by all the other evidence. They need to understand the DNA evidence isn’t the whole picture. It’s just one piece of the puzzle.

At Kammen & Moudy, LLC, our attorneys know how to address DNA evidence in a clear and accurate manner. We protect our clients through careful analysis and thorough preparation. Our clients can depend on us to make sure their rights are protected in criminal proceedings, including those where DNA evidence is a factor.

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