National Security Agency snoops are harvesting as many as 5 billion records daily to track mobile phones as they ping nearby cell towers across the globe.

That alarming scoop by The Washington Post via documents provided by NSA leaker Edward Snowden included wishful thinking from an unnamed government "intelligence lawyer" interviewed in the story. This official, according to the Post, said that the data "are not covered by the Fourth Amendment," meaning a probable-cause warrant isn't required to get it.

In reality, however, the case law on cell-site locational tracking – while generally favorable to the government – is far from clear, with federal courts and appellate courts offering mixed rulings on whether warrants are needed.

And it's a big deal. As of last year, there were 326.4 million wireless subscriber accounts, exceeding the U.S. population, responsible for 2.3 trillion annual minutes of calls, according to the Wireless Association.

All the while, warrantless cell-phone location tracking has become a de facto method to snoop on criminals in the wake of the Supreme Court's decision that probable-cause warrants from judges are generally needed to affix covert GPS devices to vehicles.

Yet the mobile-phone location data issue has never been squarely addressed by the Supreme Court, and the dispute isn't likely to be heard by the justices any time soon. All of which means that the legality of the latest crime- or terror-fighting method of choice is equally up in the air.

The high court in June rejected an appeal (.pdf) from a drug courier sentenced to 20 years after being nabbed with 1,100 pounds of marijuana in a motor home camper the authorities tracked via his mobile phone pinging cell towers for three days from Arizona to a Texas truck stop.

In that case, and without comment, the Supreme Court let stand a ruling from the 6th U.S. Circuit Court of Appeals, which covers Kentucky, Michigan, Ohio and Tennessee. The appeals court ruled that probable-cause warrants were not necessary to obtain cell-site data.

The appeals court had distinguished the case from the GPS decision decided by the Supreme Court two years ago. The high court had ruled that the physical act of installing a GPS device on a target's vehicle amounted to a search, which usually necessitates a probable-cause warrant under the Fourth Amendment.

"Here, the monitoring of the location of the contraband-carrying vehicle as it crossed the country is no more of a comprehensively invasive search than if instead the car was identified in Arizona and then tracked visually and the search handed off from one local authority to another as the vehicles progressed. That the officers were able to use less expensive and more efficient means to track the vehicles is only to their credit," the three-judge appellate panel of the 6th Circuit ruled 2-1.

According to the Post, "the NSA pulls in location data around the world from 10 major 'sigads,' or signals intelligence activity designators. A sigad known as STORMBREW, for example, relies on two unnamed corporate partners described only as ARTIFICE and WOLFPOINT. According to an NSA site inventory, the companies administer the NSA's 'physical systems,' or interception equipment, and 'NSA asks nicely for tasking/updates.'"

Regarding whether that's legal, the 5th U.S. Circuit Court of Appeals – which covers Louisiana, Mississippi and Texas – in July sided with the government in a case involving three lower court rulings concerning unidentified suspects. A lower court said "compelled warrantless disclosure of cell site data violates the Fourth Amendment."

The government argued that a mobile-phone company may disclose historical cell-site records created and kept by the company in its ordinary course of business, where such an order is based on a showing of "specific and articulable facts" that there are reasonable grounds to believe that the records sought are relevant and material to an ongoing criminal investigation. A court warrant, on the other hand, requires the higher probable-cause standard under the Fourth Amendment. The appeals court agreed. (.pdf)

The government's argument is based on a 1979 Supreme Court ruling upholding a Maryland purse snatcher's conviction. The conviction and 10-year term came after the cops compelled the phone company to make a record of the numbers dialed by defendant Michael Lee Smith. A warrant, the high court reasoned, was not required because people do not have a reasonable expectation that the records they maintain with businesses would be kept private.

That same case has provided the legal justification for the NSA's massive phone-metadata snooping program.

Still, another appellate court to have ruled on the issue was the 3rd U.S. Circuit Court of Appeals. The appellate court said in 2010 that the lower courts have the option to demand a warrant for cell-site data. The court covers Delaware, New Jersey and Pennsylvania.

Meanwhile, U.S. District Judge Richard Bennet of Maryland last year cited the purse-snatching decision when declining to suppress evidence that Aaron Graham and Eric Jordan were allegedly involved in a string of Baltimore City fast-food restaurant robberies. They were arrested in connection to one robbery, and a 7-month historical look of their phone records placed them on the scene when other restaurants were robbed, the authorities said.

Bennet ruled:

For the following reasons, this Court concludes that the Defendants in this case do not have a legitimate expectation of privacy in the historical cell site location records (.pdf) acquired by the government. These records, created by cellular providers in the ordinary course of business, indicate the cellular towers to which a cellular phone connects, and by extension the approximate location of the cellular phone. While the implications of law enforcement’s use of this historical cell site location data raise the specter of prolonged and constant government surveillance, Congress in enacting the Stored Communications Act, has chosen to require only ‘specific and articulable facts’ in support of a government application for such records.

That decision is on appeal with the 4th U.S. Circuit Court of Appeals, which covers Virginia, West Virginia, North Carolina and South Carolina. Oral arguments are slated for next month.