Today the U.S. Supreme Court hears arguments in Maryland v. King, the Court’s latest foray into DNA testing. Most reports have focused on the clash between law enforcement’s desire to test every arrested person in order to try to solve old cases, and those who advocate for a strict interpretation of the Fourth Amendment’s protection of privacy. For example, a report by the excellent Nina Totenberg of National Public Radio discussed the positions of police, who believe taking a sample from every person arrested is a minimal intrusion that can have a big payoff, and the arguments of defense attorneys and civil libertarians, who feel that allowing testing of all arrestees would surrender the basic principles of the Fourth Amendment’s protection against unlawful searches and seizures.
But there’s a question that may be far more important: from a crime fighting point of view, is it a good idea for police to take and process a DNA sample for everyone who gets arrested? Of course there will be some cases — such as the King case itself — in which the time-of-arrest sample leads to an arrest for a different, serious crime. But taking samples from every arrestee may actually hurt our efforts to use DNA most effectively to make ourselves safe. According to an article in Slate by Brandon Garrett and Erin Murphy, real public safety gains from DNA lie not with taking samples from every jaywalker and burglar and hoping for a hit in a cold case, but instead in taking many more samples from crime scenes. In other words, we get more hits when we process samples from active crime scenes and match them against our already-large DNA database, instead of fishing for leads among the whole population of more than 12 million people arrested every year. And all of those additional samples from arrestees crowd out and slow down the processing of samples from real crime scenes and victims, creating backlogs. In other words, bigger DNA databases is not the answer to crime.
[B]igger 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….The police solve more crimes not by taking DNA from suspects who have never been convicted, but by collecting more evidence at crime scenes. Even worse, taking DNA from a lot of arrestees slows the testing in active criminal investigations….Backlogs created by arrestee DNA sampling means that rape kits and samples from convicted offenders sit in storage or go untested.
The bottom line: even if the Supreme Court says we can take a sample from every person arrested, doesn’t mean we should.