The United States Supreme Court handed down an important Fourth Amendment ruling Monday that says law enforcement must obtain a warrant before hiding a global positioning system device on a vehicle during a criminal investigation, at least in some cases. The high court, however, may have left some questions about the scope of Fourth Amendment protection in technological cases for future decisions.

The current case grew out of an East Coast drug crime investigation. Law enforcement had attached a GPS device to a man's Jeep and tracked his every movement in the personal vehicle for as long as four weeks. Police used the GPS tracking information to locate a suburban house, where authorities claimed the suspect hid illegal drugs and stashed cash. The money was purportedly linked to illegal drug sales.

The man was later convicted of conspiracy to distribute cocaine and sentenced to life in prison. A federal appellate court reversed the conviction and the U.S. Supreme Court took on the issue for review.

In November this blog reported that, at oral argument in the case, some of the justices appeared uneasy about allowing law enforcement to hide GPS devices on vehicles without warrants during investigations into alleged drug crimes. Monday, all nine justices agreed that the alleged drug crime investigation at issue included an unreasonable search. However, the justices used different avenues to reach that overall conclusion.

Justice Antonin Scalia wrote the majority decision, which is binding law on all federal and state courts, including courts in the Los Angeles area. Scalia says that the government had unlawfully intruded on the defendant's rights when it attached the GPS device on the Jeep, which was sitting in a public parking lot at the time. Scalia says, "The government's physical intrusion on the Jeep for the purpose of obtaining information constitutes a search."

However, Justice Samuel Alito wrote a concurring opinion, disagreeing that the attachment of the GPS device was not itself an illegal "search" under the constitution. Alito says the illegal search occurred when the use of the GPS device began to intrude on the defendant's reasonable expectation of privacy, but declined to identify when that line was crossed. Alito says, "We need not identify with precision the point at which the tracking of this vehicle became a search, for the line was surely crossed before the 4-week mark."

Justice Sonia Sotomayor also wrote a concurring opinion. She agreed with many of the points of the two other written analyses, however, Sotomayor says the privacy expectations of suspects are important regardless of whether a hidden GPS device is being used in today's technological world. She says that police may very well invade a suspect's right to privacy by accessing signals from the person's GPS-enabled smartphone.

Source: USA Today, "Supreme Court rules warrant needed for GPS tracking," Joan Biskupic, Jan. 23, 2012