DNA evidence was revolutionary when it first started being used in criminal cases in the mid-1980's. Since its introduction, DNA evidence has been used to both convict individuals of crimes and exonerate people who have spent many years behind bars for a crime they didn't commit. Over the years the methods for analyzing DNA has become more and more sophisticated to the point that DNA profiles can be found in just a few skin cells and from a mixture of multiple individuals. However, these types of methods may not be as reliable as others. Because inaccurate results could potentially result in the convictions of innocent individuals, the National Institute of Standards and Technology (NIST) is conducting a study on these newer DNA methods. Specifically, “[t]he study will focus on DNA mixtures involving three or more people, and on very small quantities of DNA also knows as touch DNA.”
According to NIST, the “process for interpreting DNA mixtures and touch DNA can be subjective, and there are currently no clearly defined standards for doing so.” As such, “analysts might come to different conclusions given the same evidence.” NIST states that the “goal of the study is to measure the reliability of DNA profiling methods when used with different types of DNA evidence such as two-person versus four-person mixtures, and with different quantities of touch DNA.” In addition to looking at DNA technology, the study will also look at the quality control systems and training that is needed “to support the people who collect and analyze the evidence.”
With regards to multiple DNA sources, according to NIST, “[r]igouous scientific studies have shown that when the evidence contains DNA from only one or two people, DNA profiles are extremely reliable” Issues arise when the DNA evidence contains the DNA of “three or more people.” With this type of evidence, “it can be difficult to tease apart the different profiles, or in some cases, to even determine how many profiles are present.”
With regard to touch DNA, nowadays “investigators no longer need a blood or semen stain to generate a DNA profile.” Because DNA tests are so sensitive, “labs will sometimes attempt to generate a DNA profile from, for instance, a few skin cells left behind when someone touched something at a crime scene.” However, the drawback to this method is “the data can end up including meaningless information or ‘noise,' that makes it difficult to interpret.” NIST notes in modern police investigations, “[m]any police agencies now routinely swab doorknobs and other surfaces for touch DNA when investigating property crimes.” A doorknob or other surface may contain many different samples if many people have touched the surface and the result of analysis of the sample “may be a complex, low-level DNA mixture that is difficult, or impossible, to interpret reliably.”
The results of this study can be used by “crime laboratories, the courts and other institutions . . . to decide which methods pass muster.” In addition, NIST is hoping to “build a framework that will be extendable to other forensic methods.”
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