Maryland, and the other 49 states, argue that DNA collection is essential to help correctly identify arrestees and solve crimes, since it allows for more accurate identification than fingerprinting or other methods. (Some of you have asked what types of serious crimes police can collect DNA on. Some states allow collection for any type of felony; other states limit collection to violent or sexual crimes.) The federal DNA database has helped solve thousands of crimes by linking evidence from unsolved cases to people who have been arrested months or years after the trail has gone cold.

Jayann Sepich's daughter Katie was brutally raped and murdered in 2003 in New Mexico, but her killer was not identified until three years later, after he was imprisoned for an unrelated offense. "Many, many times violent offenders are arrested but are not convicted immediately, or just plead guilty to a misdemeanor, and they continue to murder and rape again and again," says Sepich, who has since founded DNA Saves, an organization that got New Mexico to pass a DNA testing law in 2007, and continues to push for similar laws around the country.

Civil-liberties advocates say that the utility of DNA collection doesn't mitigate the unconstitutionality of swiping genetic information without permission. "Police justify their collection of DNA as being helpful in efforts to solve and prevent crime," says Steven Benjamin, president of the National Association of Criminal Justice Lawyers. "The problem is that just because a technique permits more effective police work, it doesn't absolve the constitutional problems. Taking DNA from mere arrestees is undeniably absolutely unconstitutional."

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