In light of N.J. shooting, how easily can police trace 911 calls made from cell phones?

GPS coordinates and cell tower

GPS coordinates and cell tower "triangulation" are used to establish a caller's location. (Bastiaan Slabbers for NewsWorks)

Around midnight on Friday, when 76-year-old Gerald Sykes came downstairs, shotgun in hand, to confront what he thought was a pair of intruders, it probably didn’t enter his mind that the men outside were police.

The two New Jersey state troopers shining flashlights into his Upper Deerfield home were following up on a 911 hang-up made from Sykes’ house.

In minutes, Sykes would be shot three times and one of the state troopers would suffer a graze wound, either from a shotgun bullet or a shard of glass, when Sykes fired once through his sliding glass door. (Investigators say it’s not yet clear who shot first.)

But no one in Sykes’ house had made the 911 call, according to the state attorney general’s office, which said the home address used by the responding officers was “later determined to be incorrect.”

The incident calls into question the ability of law enforcement agencies in New Jersey — and nationwide — to accurately locate 911 calls and texts made from wireless devices.

“It’s a wonderful tool. As a matter of fact, it’s a tool used in virtually all walks of life,” said South Jersey forensics expert Patrick Cronin of wireless geolocation. But “there’s human error, and then there could be errors introduced by different methodologies of estimating location.”

Cronin said law enforcement officials can geolocate wireless devices using two primary methods. The first is pinpointing the device’s GPS, or Global Positioning System, coordinates.

The second involves the wireless carrier “triangulating” the device by “using two or three different towers [to] measure the time it takes for a signal to get to and from the handset.

“That can be accurate,” said Cronin, “but it’s a little more difficult.”

It’s unclear what happened in Upper Deerfield over the weekend. A Google Earth view of Sykes’ home does not appear to show any other dwellings in a 50-meter radius, the standard window used for geolocation by wireless carriers.

The state attorney general’s shooting response team is investigating the incident.

The Federal Communications Commission estimates that 70 percent of 911 calls are made from wireless phones, and that percentage is only increasing.

And the ability of officials to geolocate those calls apparently varies dramatically.

A recent investigation by USA Today and other Gannett newspapers and television stations found that wireless carriers across the country could get a fix on cell phones that called 911 anywhere between 10 percent and 95 percent of the time.

The FCC and the four major wireless carriers recently developed new goals to increase the quality of 911 cell phone geolocation.

By 2021, wireless providers must be able to provide a location within 50 meters for 80 percent of 911 calls.

Broadening its wireless 911 access even further, New Jersey last month completed a statewide rollout of text-to-911 capabilities in each of the 21 counties.

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