If you’re a student of the privacy and tech law worlds (or you just read Ars) then you’re probably familiar with last year’s Supreme Court decision, United States v. Jones. Earlier this year, the nine justices unanimously agreed that placing a GPS tracking device on a suspect’s car without a warrant was unconstitutional. That decision continues to have ripple effects throughout the privacy law world, and likely will for years to come.

However, as we pointed out in our January 2012 coverage, the justices disagreed amongst themselves about why it violated the Fourth Amendment, which protects citizens against unreasonable searches and seizures. One wing of the court found that installing the GPS device was an unwarranted physical trespass on private property and therefore illegal. The minority wing found the practice unconstitutional as it violated the doctrine known as “a reasonable expectation of privacy.”

In Jones, the Supreme Court found the act of installing the GPS tracking device was a Fourth Amendment search, and doing so without a warrant in that case was unconstitutional. However, the court did not consider the question of whether a warrant—and probable cause—is always required when the government uses a GPS device. In a new case, known as United States v. Robinson, the government argues that an officer’s mere “reasonable suspicion” of wrongdoing is enough to justify the placement of a GPS tracking device on a suspect’s car without a warrant. Earlier this year, a federal magistrate judge in Missouri agreed, allowing evidence collected by the GPS device to stand.

Last week, the American Civil Liberties Union (ACLU) filed an amicus brief in the case, which is still being argued before the United States District Court in the Eastern District of Missouri. The ACLU argues that Jones bolsters its position that “[t]his Court should adhere to the Supreme Court’s long-standing directive that warrantless searches are presumptively unreasonable and hold that defendant’s Fourth Amendment rights were violated.”

It is highly unusual for an outside group to file an amicus brief in a criminal case at such an early stage, but the ACLU appears to believe Robinson is a serious violation of criminal procedure warranting its attention.

In this case, the magistrate judge’s acceptance of the GPS device might indicate the district court judge could also allow this evidence at trial. That may potentially pave the way for a federal appeals court ruling. A future appeals court decision could turn on precisely this point: what, if any, legitimate circumstances exist in which law enforcement may affix a GPS tracking device without first obtaining a warrant?

Defendant argued to suppress GPS evidence

The case involves a man named Fred W. Robinson of St. Louis, charged with improper use of public funds between 2006-2010. Robinson allegedly falsified documents that allowed him to receive a paycheck from the City of St. Louis. During the course of the investigation, starting in 2009, the FBI began an investigation of Robinson and started observing him, his car, and his property to find out he was, in fact, an employee of the city. By January 2010, the FBI put a GPS tracking device on Robinson’s car without a warrant, leaving it running 24 hours a day for nearly two months. Robinson was indicted on federal fraud charges in 2011. As the ACLU points out, the duration of GPS surveillance was twice as long as the case in Jones.

Robinson’s attorneys argued, among other things, that the collection of evidence by the GPS device was an unreasonable search and should be suppressed.

In March, the United States Attorney (the prosecutor in the case) argued in a response (PDF) that “neither a warrant nor probable cause should be required where the agents have reasonable suspicion,” and that a “requirement of a warrant and probable cause would seriously impede the government's ability to investigate leads and tips on drug trafficking, terrorism, and other crimes. Law enforcement officers could not use GPS devices to gather information to establish probable cause, which is often the most productive use of such devices.”

The defendant’s pretrial motion was denied in May by the federal magistrate judge (PDF).

“In this case, the investigating agents had reasonable suspicion to believe that defendant had engaged in and was engaging in criminal activity, namely, submitting false time sheets to be paid for work not performed,” wrote US Magistrate Judge David D. Noce.

“Prior to installing the GPS tracking device, Agent Comeau interviewed four long-time former employees of the Treasurer’s Office, Curtis Royceton, Dan Parsons, Ben Philips, and Harold Miner, each of whom provided information supporting the investigating agents’ suspicion.”

According to the St. Louis Post-Dispatch, earlier this year, Agent Comeau said during a pretrial hearing that “in 17 years with the FBI, she had never had occasion to install a GPS tracking device before, but it was approved by prosecutors and her supervisors, based on case law at the time.”

The judge appears to have agreed with this line of reasoning, and goes on to describe the specific information provided to the FBI, concluding that this was indeed a reasonable suspicion.

“The agents believed that tracking the movements of defendant’s vehicle would enable them to confirm or dispel their suspicion,” the judge wrote. “By tracking defendant’s vehicle, the agents would be able to observe defendant’s daily pattern accurately and cost-effectively. Therefore, the agents did not need to obtain a judicial warrant prior to installing the GPS tracker device on defendant’s vehicle and using the device to monitor the vehicle’s movements. The evidence obtained from the GPS tracker device should not be suppressed for lack of reasonable suspicion.”

The magistrate judge, as a part of federal jurisprudence, must rule on pretrial motions, such as this one, setting the stage for a criminal trial. However, any decisions on acceptance or suppression of evidence by the magistrate, of course, must be approved by the district judge before they take effect during trial.

ACLU rejects government argument

In arguing that the GPS evidence should be suppressed, the ACLU argues primarily that the FBI agents violated Robinson’s Fourth Amendment rights.

The ACLU attorneys write based on judicial precedent, that warrantless searches are presumed to be unreasonable, outside of a few well-defined exceptions, such as “exigent circumstances.” This is the principle that gives, for example, a law enforcement agent the authority to enter a private property if he or she hears someone being violently attacked. Here, the ACLU cites cases, including Jones, holding that warrants are required to provide a judicial check on the abuse of law enforcement power.

ACLU counsel goes on to argue that Magistrate Judge Noce’s understanding of the appeals court decision is flawed, as it does not take into account the Jones decision. Noce cited United States v. Marquez, a pre-Jones federal appeals court decision, which found that installing a GPS tracker was not a search. Later, Jones clearly found that installing a GPS device on a car was indeed a Fourth Amendment search. Worse still, the amicus points out, “The Eighth Circuit’s decision in Marquez was not issued until four months after the agents engaged in the GPS tracking in this case.”

Finally, the ACLU also argues that no exceptions to the warrant requirement apply, arguing that “prolonged GPS tracking over a period of months is by definition the antithesis of an ‘exigent circumstance.’” In other words, because the government knew that it could track Robinson over a long period of time, that meant there was no immediate need to conduct a search.

The Robinson case is ongoing. A decision likely will take several more months, but it could provide more precision concerning when law enforcement can and can’t track suspects without a warrant.