Like millions of motorists, Eric Hanson used a Global Positioning System unit in his Chevrolet TrailBlazer to find his way around. He probably didn’t expect that prosecutors would eventually use it too — to help convict him of killing four family members.
Prosecutors in suburban Chicago analyzed data from the Garmin GPS device to pinpoint where Hanson had been on the morning after his parents were fatally shot and his sister and brother-in-law bludgeoned to death in 2005. He was convicted of the killings this year and sentenced to death.
Hanson’s trial was among recent criminal cases around the country in which authorities used GPS navigation devices to help establish a defendant’s whereabouts. Experts say such evidence will almost certainly become more common in court as GPS becomes more affordable and show up in more vehicles.
“There’s no real doubt,” said Alan Brill, a Minnesota-based computer forensics expert who has worked with the FBI and Secret Service. “This follows every other technology that turns out to have information of forensic value. I think what we’re seeing is evolutionary.”
For years, police have been able to trace cellphone signals and use other dashboard devices such as automatic toll-collection systems to confirm a driver’s whereabouts.
But the growing popularity of GPS units — in cars, phones and other hand-held devices — gives authorities another powerful tool to track suspects.
Among recent cases:
• In September, a man in Butte, Mont., pleaded guilty to rape shortly after a judge ruled that evidence from the GPS unit in his car could be used against him at trial. Prosecutors planned to use it to show that Brian D. Adolf “prowled” through town looking for a victim.
• In New Brighton, Pa., a trucker’s GPS led police to charge him with setting his own home on fire. GPS records showed his rig was parked about 100 yards from his house at the time of the fire.
The Consumer Electronics Association estimates 20 percent of American households own a portable GPS unit and 9 percent have vehicles equipped with in-dash systems.
Detectives are often able to extract map searches and desired destinations that have been entered into a GPS unit by the user. Some devices are equipped with a “track back” feature that can show where the unit was at a particular time.
“What we’re dealing with here is a use of the technology that I don’t think the good people at Magellan or Garmin or TomTom really thought about when they were developing it,” said Brill, referring to manufacturers of GPS devices.
