Research shows that bigger is only better if DNA databases grow in the right way: by entering more samples from crime scenes, not samples from arrestees. DNA databases already include 10 million-plus known offender profiles. But a database with every offender in the nation cannot solve a crime if no physical evidence was collected or tested. And police collect far too few such samples.
Even worse, taking DNA from a lot of arrestees slows the testing in active criminal investigations. After all, 12 million or more people are arrested each year. (According to one study, by age 23, nearly one-third of Americans have been arrested for an offense, not including minor traffic violations.) Backlogs created by arrestee DNA sampling means that rape kits and samples from convicted offenders sit in storage or go untested.
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 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.