DNA’s crime-fighting role

This week it was announced that DNA testing of bones found buried beneath a parking lot in Leicester, England, had established that they belonged to King Richard III, who was killed in battle in 1485. Researchers were able to match DNA recovered from the skeleton with that of a living descendant of the much-vilified monarch’s sister. The find was just the latest reminder of the immense power of DNA evidence, power that is expanding history and criminal justice but that also is subject to misuse.

Indeed, DNA technology has been instrumental in resolving more-contemporary mysteries. According to the Innocence Project, DNA evidence has resulted in the exoneration of more than 300 Americans convicted of crimes, including 18 who had served time on death row. On the opposite side of the ledger, DNA evidence has been used to convict the guilty. It’s the latter use of DNA information that figures in a case to be argued before the Supreme Court this month.

Supported by virtually every other state, the Obama administration and local officials, including the district attorney of Los Angeles County, the state of Maryland is seeking court approval for taking DNA samples from individuals arrested for serious crimes and checking that information against a database that includes evidence from unsolved crimes. The court should decline the request and affirm a ruling by Maryland’s highest court that taking DNA samples from persons who haven’t been convicted of a crime violates the 4th Amendment’s ban on illegal searches and seizures.

Several arguments for acquiring such information are being offered: that, like taking fingerprints, collecting DNA helps police to make sure a suspect is who he says he is; that, by revealing whether a suspect committed a violent crime in the past, it can shape decisions about whether the government should oppose bail; and that it is minimally intrusive, requiring only that a suspect swab the inside of his cheek.

But the most emotionally compelling argument for acquiring DNA at the time of an arrest is that it might implicate the suspect in another crime and help bring him to justice.

The problem is that the 4th Amendment has traditionally required probable cause or at least reasonable suspicion before a search is conducted; the fact that someone has been arrested on suspicion of one crime doesn’t create probable cause that he committed another. Unless he is convicted, he should have the same protection against unreasonable searches enjoyed by individuals who haven’t been arrested (even though taking DNA samples from some of them might also clear up unsolved crimes). That may not be a popular conclusion, but it’s the correct one.