The conflicting tug of personal privacy and crime-solving technology tore at the Supreme Court on Tuesday as justices considered whether the Fourth Amendment permits police to take DNA samples from arrestees who have not been charged with or convicted of a crime.

Justices appeared unusually burdened by the gravity of the issue. At one point Justice Samuel Alito Jr. said he believed the case before them, Maryland v. King, was "perhaps the most important criminal procedure case that this court has heard in decades."

The libertarian streak of some of the court’s conservatives was on display, with justices expressing worry about the implications of a Maryland law—similar to those in 27 other states—that does not require a search warrant before police can use a swab to take a DNA sample from inside the mouths of those arrested for serious crimes.

Justice Antonin Scalia set the tone in the opening moments of the hour-long argument, after Deputy Maryland Attorney General Katherine Winfree rattled off the number of convictions obtained and crimes solved when DNA collected under the law matched DNA gathered in previous crimes.

"Well, that’s really good!" Scalia exploded. "I’ll bet if you conducted a lot of unreasonable searches and seizures, you’d get more convictions, too. That proves absolutely nothing."

Briefly flustered, Winfree hesitated but then said the numbers proved the statute was working.

Soon, other justices piled on, with Chief Justice John Roberts Jr. asking why, if Maryland’s law was constitutional, the DNA sampling couldn’t be expanded to those arrested for less serious crimes. Why not "anybody pulled over for a traffic violation," he asked. What about a Terry stop, asked Justice Ruth Bader Ginsburg, referring to the Terry v. Ohio ruling that allows police to stop and frisk citizens based on only "reasonable suspicion" that the person is armed or might have committed a crime.

Justice Elena Kagan wondered why, if police can take DNA of an arrestee, they couldn’t also search that person’s home. "Just because you’ve been arrested doesn’t mean that you lose the privacy expectations in things that you have that aren’t related to the offense that you’ve been arrested for," Kagan stated, adding, "Why don’t we do this for everybody who comes in for a driver’s license?" Justice Sonia Sotomayor worried that the law could be extended to "schools, workplaces, wherever else the state has control over your person."

Winfree responded to the barrage by asserting that when police arrest someone, that person "surrenders a substantial amount of liberty and privacy." That lessened expectation of privacy allows police to take DNA not only for the purposes of solving other crimes but also to determine a suspect’s identity and past record and, if a match is made, whether the suspect should be let out on bail.

That led to another wave of skepticism from Sotomayor and others, based on the fact that unlike fingerprints, DNA samples take weeks or months to process under current technology—long after a bail decision is usually made. Winfree gamely said that even if the arrestee has been released on bail by the time the DNA sample comes back from the laboratory, bail could be revoked.

The attacks from the court seemed to leave the Maryland law in tatters—until Deputy Solicitor General Michael Dreeben rose in support of DNA sampling. Dreeben, the long-time expert on criminal law for the SG’s office, changed the dynamics of the argument when he told the court, "The future is near where there will be rapid DNA analyzers that are devices that can analyze and produce the identification material in the DNA within 90 minutes. And the design of the program is to put them at the booking station so that DNA can be taken and within 90 minutes that information is known."

Suddenly, DNA sampling began to look to the justices like fingerprinting, which has long been viewed as constitutional. If the DNA sample could be processed that quickly, then it could be justified as a method of verifying the identification of the suspect and of informing the bail decision.

Dreeben’s description of the future also changed how the justices questioned Kannon Shanmugam of Williams and Connolly, the lawyer for Alonzo King, the defendant in the case. When King was arrested on assault charges in 2009, police routinely took a DNA sample that linked him to a rape six years earlier. King sought suppression of the DNA evidence, and the Maryland Court of Appeals ruled in his favor, finding that the DNA was not needed by police for the initial arrest. As a result, the court ruled, King had a "sufficiently weighty and reasonable expectation of privacy" that was not outweighed by the state’s interest.

"Why isn’t this the fingerprinting of the 21st century?" asked Alito. "What is the difference?" Shanmugam said fingerprinting is less intrusive, reveals less information, and "serves a special need," namely verifying the identity of the arrestee.

But Kagan, citing Dreeben’s comments, said the government’s position is, "Give us five years and this won’t look very different…so give us a break."

Shanmugam agreed the "analysis would be different" when DNA analysis is more immediate. But for now, if police want to investigate other crimes, "they have to do what they would have to do as an ordinary citizen."

The debate seemed to leave justices in a quandary. When Maryland’s Winfree rose again in rebuttal, Roberts asked with seeming exasperation, "You say, in two years we will have this rapid DNA available, but we don’t now. Don’t I have to base a decision on what we have today?"

Tony Mauro can be contacted at tmauro@alm.com.