Over the last few decades, DNA evidence has revolutionized many aspects of the criminal justice system, helping to convict the guilty and free the innocent. Initially, DNA was used simply to confirm or dispel an already-identified suspect’s guilt in a case where there was some question about the identity of the perpetrator: A DNA sample from a crime scene was compared to the suspect’s DNA. If the samples matched, that was further evidence of guilt; if they did not match, that was evidence against guilt. But as the costs of DNA analysis decreased and the prevalence and capacity of networked computer systems increased, law enforcement began to use DNA in a very different way, compiling enormous databanks of standardized DNA profiles from known individuals and comparing them to a databank of profiles generated from crime-scene samples. In 1994, Congress authorized the Department of Justice to create a federal databank, the National DNA Index System, or NDIS, which started operating in 1998. 

Since then, these databanks have expanded hugely: they initially contained only profiles taken from persons convicted of very serious crimes such as murder or rape. Now, they contain profiles taken from people merely arrested for crimes such as shoplifting, simple drug possession, and even for minor traffic offenses committed on federal land. Because of the legal and practical barriers to having profiles removed from the database, these samples will almost certainly remain in the database permanently, even if the arrestee is never convicted or even charged with a crime.  

Furthermore, the databanks are no longer used only to find exact matches between crime-scene evidence and an offender profile: with a relatively new technique known as familial searching, law enforcement uses the DNA database to focus on a person whose DNA does not match the crime-scene evidence – and who is therefore demonstrably innocent of the crime – because that profile is similar to DNA taken from a crime scene, based on the hope that the culprit may be related by blood to the known person who provided the similar sample. Thus, a person whose DNA is included in the databank may find himself subject to having his sample further analyzed at any time in the future simply because it is similar to one found at a crime scene. And, if this further analysis fails to show that he is not related to the person who left the sample at the crime scene, he – and his family – may well be subject to other forms of investigation as well.  

This expansion of the size, scope, and use of DNA databanks raises a number of questions about individual and familial privacy, the presumption of innocence, and the power of the government to seize, analyze, and store our genetic profile. It also may serve to magnify the racial disparities that are already present in our criminal-justice system and provide a new incentive for pretextual arrests to obtain a DNA sample. And the expansion of these programs to include people merely arrested for minor offenses – approximately 1/3 of whom will never be convicted of anything and many of whom may well be completely innocent – raises additional concerns about the waste of scarce resources in databanking the DNA of innocent persons. 

The ACLU-Northern California has filed a lawsuit in federal court seeking to stop California's policy of mandating that DNA is collected from anyone arrested for a felony, whether or not they are ever charged or convicted. The web page describing the suit contains links to more resources on this topic.