Putting DNA from arrestees into databanks also exposes more innocent people to the risk of false accusation or conviction. Interpretation of DNA evidence from known offenders is straightforward, but crime scene samples often require subjective judgments that may lead to errors. What is more, cross-contamination and accidental sample switches have occurred in labs across the country. In one case in Nevada, a man spent four years in jail because an analyst accidentally switched his sample. In three more cases, erroneous DNA testing led to wrongful convictions that were overturned by subsequent DNA tests. A 2009 National Academy of Science report criticized the current lack of quality control in the forensic testing system. But improvement seems less likely if crime labs are inundated with DNA from arrestees. The FBI has also opposed confidential access for researchers who could independently assess government assertions about the accuracy of DNA databases.
In addition, arrestee testing exacerbates the racial disparities in DNA databases. Because African-Americans and Hispanics make up a disproportionate share of convicts, they are overrepresented in databases. Racial disparities in arrest rates, particularly for minor crimes like drug possession, can be even starker. Allowing states to bank DNA of arrestees will mean including disproportionate amounts of genetic information from African-Americans and Hispanics as compared to other groups.
King's case may seem like a poster-child for DNA database expansion, because his sample closed a serious unsolved case. But there is more to the story. King had at least six prior convictions at the time of his sentencing for the shotgun offense. A state law limited to taking DNA from convicted offenders could have authorized his testing. The same is true of dozens of other arrestee DNA "success stories."
That suggests that the line between arrest and conviction is the right place to locate the constitutional limit on the government's unending appetite for collecting our DNA. If the Supreme Court approves Maryland's law, then DNA samples will be routinely taken from people upon arrest just like fingerprints. Unlike fingerprints, however, the DNA samples will be used not to identify people, but to forever implicate them as one of the "usual suspects." Also unlike fingerprints, DNA samples convey a lot of information, like your sex, what you look like, whether you are adopted, or how old you might be. Some states have even decided, without judicial approval or new laws, to use DNA databases to find not only people in the database, but also their family members. And as technology evolves, who knows what is next? What we know now is that no good evidence shows that taking from DNA from arrestees helps to solve crimes in any meaningful way. We also know the cost to liberty and privacy. That's the tradeoff the Supreme Court should weigh.