Prosectors are shifting their focus to warrantless cell-tower locational tracking of suspects in the wake of a Supreme Court ruling that law enforcement should acquire probable-cause warrants from judges to affix GPS devices to vehicles and monitor their every move, according to court records.

The change of strategy comes in the case the justices decided in January, when it reversed the life sentence of a District of Columbia area drug dealer, Antoine Jones, who was the subject of 28 days of warrantless GPS surveillance via a device the FBI secretly attached to his vehicle. In the wake of Jones' decision, the FBI has pulled the plug on 3,000 GPS-tracking devices.

In a Friday filing in pre-trial proceedings of Jones retrial, Jones attorney' said the government has five months' worth of a different kind of locational tracking information on his client: So-called cell-site information, obtained without a warrant, chronicling where Jones was when he made and received mobile phone calls in 2005.

"In this case, the government seeks to do with cell site data what it cannot do with the suppressed GPS data," attorney Eduardo Balarezo wrote (.pdf) U.S. District Judge Ellen Huvelle.

Balarezo added:

The government has produced material obtained through court orders for the relevant cellular telephone numbers. Upon information and belief, now that the illegally obtained GPS data cannot be used as evidence in this case, the government will seek to introduce cell site data in its place in an attempt to demonstrate Mr. Jones' movements and whereabouts during relevant times. Mr. Jones submits that the government obtained the cell site data in violation of the Fourth Amendment to the United States Constitution and therefore it must be suppressed.

Just as the lower courts were mixed on whether the police could secretly affix a GPS device on a suspect's car without a warrant, the same is now true about whether a probable-cause warrant is required to obtain so-called cell-site data.

A lower court judge in the Jones case had authorized the five months of the cell-site data without probable cause, based on government assertions that the data was "relevant and material" to an investigation.

"Knowing the location of the trafficker when such telephone calls are made will assist law enforcement in discovering the location of the premises in which the trafficker maintains his supply narcotics, paraphernalia used in narcotics trafficking such as cutting and packaging materials, and other evident of illegal narcotics trafficking, including records and financial information," the government wrote in 2005, when requesting Jones' cell-site data.

That cell-site information was not introduced at trial, as the authorities used the GPS data for the same function.

The Supreme Court tossed that GPS data, along with Jones' conviction, on Jan. 23.

The justices agreed to decide Jones' case in a bid to settle conflicting lower-court decisions – some of which ruled a warrant was necessary, while others found the government had unchecked GPS surveillance powers.

"We hold that the government's installation of a GPS device on a target's vehicle, and its use of that device to monitor the vehicle's movements, constitutes a 'search,'" Justice Antonin Scalia wrote for the five-justice majority.

The government has maintained in a different case on appeal that cell-site data is distinguishable from GPS-derived data. District of Columbia prosecutors are expected to lodge their papers on the issue by Apr. 6 in the Jones case.

Among other things, the government maintains Americans have no expectation of privacy of such cell-site records because they are "in the possession of a third party" (.pdf) – the mobile phone companies. What's more, the authorities maintain that the cell site data is not as precise as GPS tracking and, "there is no trespass or physical intrusion on a customer's cellphone when the government obtains historical cell-site records from a provider."

In the Jones case, the Supreme Court agreed with an appeals court that Jones' rights had been violated by the month-long warrantless attachment of a GPS device underneath his car. Scalia's majority opinion, which was joined by Chief Justice John Roberts, and Justices Anthony Kennedy, Clarence Thomas and Sonia Sotomayor, said placing the device on the suspect's car amounted to a search. (.pdf)