The US Supreme Court heard argument Tuesday in a case testing whether government officials can routinely collect a person’s DNA at the time he or she is arrested and then use that DNA sample to try to link the individual to unsolved crimes.

At issue in the case, Maryland v. King (12-207), is whether taking a DNA sample from an arrestee without first obtaining a court-authorized warrant is an unreasonable search under the Fourth Amendment.

DNA has become an essential law-enforcement tool, not just in its ability to conclusively identify an individual but, more important, through its ability to conclusively link suspects to cold cases.

In effect, DNA is becoming in the 21st century what fingerprinting was to the 20th – except better.

But there’s a problem. Unlike a fingerprint, DNA material contains a plethora of highly personal information bound within a person’s genetic code. When the government seizes DNA material, it is taking control of more than just the ability to isolate an identifying pattern unique to one individual. With advances in genetic science, DNA might someday reveal information about an individual’s susceptibility to future diseases and perhaps even personality traits, scientists say.

Several justices expressed concern that seizing a DNA sample from an individual to solve cold cases is a search under the Fourth Amendment. What justifies the state taking such action without a warrant?, they wanted to know.

Katherine Winfree, Maryland’s chief deputy attorney general, told the justices that the state did not need to obtain a warrant to collect DNA samples from arrestees because people in police custody have already surrendered a substantial amount of their liberty and privacy.

“That can’t quite be right,” Justice Elena Kagan countered. “Assume you’ve been arrested for something; the state doesn’t have a right to go search your house for evidence of unrelated crimes.”

She added: “Just because you’ve been arrested doesn’t mean that you lose your privacy expectations ... that aren’t related to the offense that you’ve been arrested for,” Justice Kagan said.

“What we’re seizing is not evidence of crime,” Ms. Winfree responded. “What it is is information related to that person’s DNA profile.”

One issue in the case is the purpose of collecting the DNA. Maryland uses it to help identify the arrestee, Winfree said. But the state also uses it to solve unsolved crimes.

Justice Sonia Sotomayor picked up the same line of questioning. “You are going to have to tell me why searching their person is different than searching their home or car,” she said.

Winfree replied that people in police custody have a reduced expectation of privacy that eliminates Fourth Amendment protections for a person’s DNA. Collecting the DNA sample, she added, is minimally intrusive, involving a buccal swab from the inside of an arrestee’s cheek.

Michael Dreeben, deputy US solicitor general, told the justices that taking a DNA sample was substantially different from searching a home for evidence of a crime. “It is far more like taking a fingerprint,” he said.

Both federal and state laws bar agencies from using stored DNA samples to analyze data for anything other than the identifying information, Mr. Dreeben said. An individual would retain a reasonable expectation that the rest of the DNA sample would remain private, he said.

According to Kagan, verifying a fingerprint match can take a matter of minutes, while Maryland’s DNA tests take on average 11 to 17 days to complete.

Dreeben responded that the expectation is that within two years, police will have DNA analyzers in police booking stations capable of completing an identification within 90 minutes.

Not all justices were skeptical of Maryland’s DNA statute. Justice Samuel Alito observed that police had long been permitted to routinely take fingerprints of suspects upon arrest, and it wasn’t clear why the same couldn’t be done with DNA swabs.

“I think this is perhaps the most important criminal procedure case that this court has heard in decades,” he said.

“The attorney for the state began by listing a number of crimes just in Maryland that had been solved using this,” he said. “So this is what is at stake: lots of murders, lots of rapes that can be solved using this new technology that involves a very minimal intrusion on personal privacy.”

Kannon Shanmugam, the lawyer challenging the Maryland statute, countered that DNA testing involves a far greater intrusion into privacy than fingerprinting.

DNA contains significantly more information and significantly more personal information than a set of fingerprints, he said. In addition, no one has an expectation of privacy in his or her fingerprints, which are left on surfaces wherever the person goes. So unlike taking a buccal swab, collecting fingerprints at the police station is not considered a search for purposes of the Fourth Amendment, he said.

Forty-nine other states, the District of Columbia, Puerto Rico, and the federal government filed briefs in support of Maryland’s DNA collection statute.

The debate over DNA collection stems from the case of Alonzo Jay King, who was arrested in Wicomico County, Md., in April 2009 after he was accused of pointing a shotgun at a group of people. Police charged him with first- and second-degree assault.

Under the Maryland DNA law, as a recent arrestee for a serious crime, Mr. King was required to submit to a buccal swab from his cheek to collect a DNA sample.

The sample was sent to the national DNA database, where it matched DNA collected at the scene of a 2003 rape in Wicomico County, Md.

King was charged with rape and robbery in the 2003 unsolved crime. He was later convicted of first-degree rape and sentenced to life in prison.

King’s lawyer challenged the collection of the DNA evidence, arguing that police should have first obtained a warrant. The trial judge rejected the argument, but the Maryland Court of Appeals reversed. It ruled the police must first obtain a warrant before collecting DNA from an arrestee.

If King wins at the Supreme Court, it won’t necessarily mean an end to DNA testing of those within the criminal justice system. King’s lawyer concedes that the state has the power to collect DNA without a warrant from convicted criminals since a convicted criminal has a diminished expectation of privacy, below that of an arrestee.

A decision in the case is expected by June.