Perhaps no development in criminal law has been more dramatic or transformative than DNA evidence. DNA fingerprinting is now nearly unassailable and incontrovertible as evidence in court; and thousands of Americans wrongly convicted of crimes have been set free because of new DNA analysis and matching. DNA evidence helped inspire the creation of DNA databases. In the late 1980s, the federal government laid the groundwork for the Combined DNA Index System or CODIS, a system of national, state and local databases for storing and exchanging DNA profiles.

And since 1996, mitochondrial DNA has provided forensic scientists with a valuable tool for determining the source of DNA recovered from damaged, degraded or very small biological samples. But it was expert scientific witnesses who made all of that innovative evidence admissible.

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