the science behind DNA analysis is valid, a subsequent NRC report in 1996 recommended new ways of interpreting DNA evidence to help answer a key question for jurors—the likelihood that two matching samples can come from different people.12 This 1996 report recommended a set of statistical calculations that takes population structure into account, which enhanced the validity of the test. The report also called for independent retesting and made recommendations to improve laboratory performance and accountability through, for example, adherence to high-quality standards, accreditation, and proficiency testing.

Since then, the past two decades have seen tremendous growth in the use of DNA evidence in crime scene investigations. Currently more than 175 publicly funded forensic laboratories and approximately 30 private laboratories conduct hundreds of thousands of DNA analyses annually in the United States. In addition, most countries in Europe and Asia have forensic DNA programs. In 2003, President George W. Bush announced a 5-year, $1 billion initiative to improve the use of DNA in the criminal justice system. Called the President’s DNA Initiative, the program pushed for increased funding, training, and assistance to ensure that DNA technology “reaches its full potential to solve crimes, protect the innocent, and identify missing persons.”13

Thus, DNA analysis—originally developed in research laboratories in the context of life sciences research—has received heightened scrutiny and funding support. That, combined with its well-defined precision and accuracy, has set the bar higher for other forensic science methodologies, because it has provided a tool with a higher degree of reliability and relevance than any other forensic technique. However, DNA evidence comprises only about 10 percent of case work and is not always relevant to a particular case.14 Even if DNA evidence is available, it will assist in solving a crime only if it supports an evidential hypothesis that makes guilt or innocence more likely. For example, the fact that DNA evidence of a victim’s husband is found in the house in which the couple lived and where the murder took place proves nothing. The fact that the husband’s DNA is found under the fingernails of the victim who put up a struggle may have a very different significance. Thus, it is essential to articulate the reasoning process and the context associated with the evidence that is being evaluated.


National Research Council. 1996. The Evaluation of Forensic DNA Evidence: An Update. Washington, DC: National Academy Press.




The American Society of Crime Laboratory Directors. 2004. 180 Day Study: Status and Needs of U.S. Crime Labs. p. 7, table 2.

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