Graham was sitting on the passenger's side, and police found a pistol with a pearl handle under the seat and $83 cash in the center console.

Hours earlier, a man had robbed a Burger King across from Carroll Park, leaping over the counter, bashing an employee in the head with his gun butt and emptying cash drawers. About an hour after that, a man robbed a McDonald's less than two miles away.

Employees of the restaurants identified Graham as the robber and the truck as his getaway vehicle. No one identified Jordan.

After the two were charged, federal prosecutors working with the FBI asked a judge to order that Sprint turn over 221 days of phone location logs.

Investigators combed the calls Jordan and Graham made the day they were arrested. Records showed that Graham used his phone just before 3 p.m. Radio waves from his phone jumped to a cell tower at the back of the Beth Shalom Hebrew Young Men's Cemetery in Woodlawn. When Jordan answered eight seconds later, his phone was in contact with the same antenna.

Cities are thick with towers — Sprint had about 700 in Central Maryland in 2011 and each had three faces creating segments of cell coverage shaped like pie slices, according to records made public in the court case.

During that afternoon call, both men were in the same coverage segment, the records showed. Graham's and Jordan's phones also communicated with the same tower in the moments after each robbery. Those calls bounced to antennas clinging to the side of a housing complex and a rusted industrial building.

The breadth of the request — defense lawyers called it a digital "dragnet" — was designed to help police figure out whether the men could be tied to other robberies.

In his closing argument, prosecutor Benjamin Block acknowledged that the cellphone records did not make the case by themselves, but tied all the other evidence together.

"It is corroboration," he told the jury. "It's corroboration of everything else that you've heard."

But the ACLU and other privacy groups argued in court filings that the records allowed investigators to learn much more about Graham and Jordan.

"Similar data could just as easily be used to conclude from cell site data points when a person visited their doctor's office or church," the groups wrote in a supporting brief.

Prosecutors had obtained tens of thousands of call records. Block noted at the trial that Graham was a "big fan of his cellphone." Few ended up being relevant to the criminal investigation, but they did give the government a window into the men's lives, the privacy advocates say.

They pointed out that almost one-third of Graham's calls were linked to the tower and coverage segment nearest his home; others suggested times when he was accompanying his pregnant wife on doctor's visits.

As technology has offered police new ways to solve crimes, they have galloped ahead, leaving judges and defense attorneys behind. Courts have recognized that the meaning of the 223-year-old Fourth Amendment — which prohibits unreasonable searches and seizures — needs to evolve with technology, but have struggled with applying that idea in practice.

In recent years, the Supreme Court has begun to offer some guidance. In 2012, the justices ruled that investigators cannot generally place a Global Positioning System tracking device on a car without a warrant, but split on the reasons why.

The leading opinion concluded that the act of putting the tracking device on the car amounted to a search. But Justice Samuel A. Alito penned a more expansive opinion arguing that the amount of location information the device allowed the government to collect was a breach of privacy.

"Society's expectation has been that law enforcement agents and others would not — and indeed, in the main, simply could not — secretly monitor and catalog every single movement of an individual's car for a very long period," Alito wrote.

Looking to that opinion, a panel of the 11th Circuit Court of Appeals ruled in June on a Florida robbery case similar to Graham's and Jordan's. The court held that cellphone information is potentially even more revealing because a phone can move inside someone's home. So, the court ruled, police should have obtained a warrant before pulling phone tower information.

In earlier cases, two courts ruled the other way. The U.S. Justice Department is challenging the conclusion in the Florida case and has asked the 11th Circuit for another hearing.