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How DNA evidence gets compromised

If there has been one innovation that has quickly redefined the way that the criminal justice system conducts its business over the last thirty years, it has been the advent of DNA evidence and the forensic investigation methods used to unearth it. Not only has this new scientific field revolutionized the way that evidence is handled, analyzed, and weighed in courtrooms around the country, it has also captured the public imagination, with countless TV shows and movies that cover its controversies, facts, and methods in ways that are always enthusiastic, even if they are not always as accurate as they could be.

The delicate issue of collection

One of the biggest problems with DNA evidence is the issue of how samples are collected. At a crime scene, it can be nearly impossible to be sure that the DNA collected is exclusively from the time of the crime unless the collection sites are very limited, and even then there is no way to be absolutely sure that trace DNA from before the crime hasn't contaminated the sample. Even when samples can be reliably taken and exclusively traced to the time of the crime, as in DNA testing in the cases of assault, mistakes in the collection process, labeling, and other chain-of-custody issues can often make the results unreliable. Other sources of contamination can include:

  • Mislabeled lab samples
  • Mishandling
  • Human error, such as sneezing into a sample or leaving it exposed to other sources of contamination
  • Intentional manipulation

Interpretation issues

The Atlantic ran an article in June 2016 about the history of the process and the early measures taken to avoid exactly the kind of contamination discussed above. In it, a comprehensive case is made for the idea that even when collection is absolutely without fault, the reading of DNA typing results is often more subjective than the field acknowledges. This subjectivity combines with a conflict of interest in states that compensate laboratories more generously for convictions than for negative test results, creating a system whereby the objectivity of the lab is compromised by the way the state incentivizes convictions.

DNA typing is here to stay, but the field is currently undergoing something of a professional reckoning. As standards and policies adjust to make DNA testing more reliable and to reduce the likelihood of biased or compromised results, it is likely to get better, but that only happens when those within the criminal justice system challenge the conventional wisdom with research and facts. If you are dealing with criminal charges that involve DNA testing, consulting with an attorney may offer some avenues to explore.

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