Aggregated News

In April 2009, police easily arrested Alonzo J. King, Jr. in Wicomico County, Md. After King pointed a shotgun at a group of people, one of them told the police who did it, and King readily admitted his guilt. He was originally charged with felony assault and ended up pleading guilty to a misdemeanor.

This seemingly insignificant criminal case is now before the Supreme Court, with arguments later this month. That’s because of what the authorities did next. When King was arrested, police took a cotton swab of skin cells from inside his cheek for DNA testing. They did not need his DNA to link him to the shotgun incident. Instead, the police entered King’s DNA profile into both the Maryland DNA database and the FBI’s national database, CODIS. King’s profile, like all those in the database, was then automatically compared every week to evidence from all unsolved crimes. And, in fact, King’s DNA matched DNA from an unsolved sexual assault case, for which he was later convicted and sentenced to life in prison.

If Maryland had required King...