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WASHINGTON (WUSA9) -- Supreme Court justicessplit down the middle on questions about Maryland's DNA testing law.

Justice Samuel Alito called it the most important criminal procedure case before the court in decades.

The question? When and where is it appropriate for police to swab your cheek and dive deep into your DNA profile?

Maryland is now swabbing everyone arrested for a serious crime, and running those swabs through DNA cold case database. That's helped close 43 criminal cases. But the state's highest court says police went too far when they arrested Alonzo King for assault and then used his DNA swab to tie him to a rape.

The case is now before the Supreme Court, and in oral arguments, several justices asked, if police can go on a fishing expedition through your DNA before you are even convicted of a crime, where does it end? Justice Elena Kagan asked rhetorically whether the state should be allowed to take the DNA of every person who comes in for a driver's license.

"Warrantless, suspicionless searches are unconstitutional," said Kannon Shanmugam, who argued King's case before the justices. Outside the court, Maryland Attorney General Doug Gansler countered that, "DNA is the 21st century fingerprint."

In Maryland, police actually have to arrest you for a serious crime to swab you for DNA. But federal rules, and the rules in many other states, are far more sweeping. Speed on the George Washington Parkway, and the US Park Police could swab your cheek and dive deep into your DNA profile.

"We believe fingerprinting is fundamentally different because of the profound information found in an individual's DNA," said Shanmugam after the hearing.

It's another issue the pits sophisticated technology against personal privacy. And the Supreme Court is still wrestling with the right balance.

The decision is expected by June. and with Chief Justice John Roberts' tough questions for both sides, he may once again have the deciding vote.

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