U.S. Supreme Court Justice Samuel Alito called the Maryland case before the justices Tuesday the most important criminal procedure question in decades: Does the Fourth Amendment allow the state to collect DNA samples from people who have been arrested but not convicted of a crime?

Maryland Chief Deputy Attorney General Katherine Winfree was cut off immediately after she began the hourlong hearing by noting 43 convictions under the state's warrantless DNA collection program since 2009.

"Unreasonable searches" should result in numerous convictions, Justice Antonin Scalia said. "That proves nothing."

Justices on both ends of the ideological spectrum said they had difficulty understanding how letting police pull open a person's mouth to stick a swab into it to obtain evidence without a warrant was any different from allowing police to rummage through the same individual's house without a warrant.

Justices asked how far do we go? Why not take DNA samples when you get your driver's license?

Maryland is one of 28 states -- along with the federal government -- that collects DNA from people who have been arrested for various crimes.

Alito called the case the "most important criminal procedure case that we've heard in decades ... This is what's at stake. Lots of murders. Lots of rapes."

Michael R. Dreeben, deputy solicitor general for the Department of Justice, argued that the DNA testing was like fingerprinting.

Chief Justice John Roberts pointed out that people leave their DNA wherever they go -- when they take a drink of water or a drag from a cigarette.

Justice Stephen Breyer said he didn't think the test was intrusive.

The case stems from the conviction of a Salisbury, Md., man named Alonzo King Jr., who was arrested on an assault charge in 2009. As he was booked at the Wicomico County jail, law enforcement officials took a swab from the inside of his cheek to collect a DNA sample. The information was uploaded into a state database that matched his profile to an unsolved 2003 rape of a 53-year-old woman.

King was convicted of the rape and sentenced to life in prison, but the Maryland Court of Appeals last year ruled that the collection of his DNA violated the Fourth Amendment.

King's lawyer, Kannon Shanmugam, argued that law enforcement authorities should be required to get a warrant before taking the DNA.

Justice Sonia Sotomayor expressed concerns of broader privacy issues.

"There are some inherit dangers of DNA collection that are not like fingerprint collection," she said.

The Supreme Court is expected to announce its ruling before its summer recess.