DNA StrandsFeb. 22 (Bloomberg) — When Alonzo King was arrested for assault in 2009 after pointing a shotgun at several people, authorities had no reason to think he was also a rapist.

Then officials swabbed his cheek at the Wicomico County, Maryland, booking facility and ran his DNA through a nationwide database. The check linked King to an unsolved 2003 rape.

Now King’s conviction for the rape is set for argument next week at the U.S. Supreme Court, which will consider whether Maryland is violating the Constitution by collecting DNA samples from people arrested for serious crimes before they’re convicted. The court’s ruling, due by June, will be its first on the privacy of genetic information and will determine the fate of laws in at least 25 states that allow DNA collection at arrest.

“If the Supreme Court rules in favor of Maryland in this case, there will be no real limits on when the government can collect DNA,” said Jennifer Lynch, a lawyer with the San Francisco-based Electronic Frontier Foundation, which opposes the collection laws. She said that would be a “huge privacy invasion.”

Maryland argued in court papers that DNA gives police an invaluable investigative tool — the “gold standard of forensic identification.” Backers of the practice point to cases where DNA collection upon arrest might have prevented…

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