GIS Tech News #11

14 Nov, 2005 By: Kenneth Wong

Cadalyst GIS Tech NewsGIS Goes to Court

Minnesota county uses geospatial data to track trail of murder case suspect -- and ultimately put him in jail

On the morning of May 12, 2004, the trial for Troy Mayhorn, a 25-year-old Chicagoan accused of aiding and abetting in the shooting death of Nasean Jordan, began with opening statements from both sides in Clay County Courthouse, in Moorhead, Minnesota. Prosecutor Lisa Borgen's arsenal included a series of PowerPoint slides showing the locations of several calls made from the defendant's cell phone during the time of the murder. The visuals were constructed using data that indicates the locations of cell towers that facilitated the calls. Pinpointed on a map and played back chronologically, the data looked like virtual footsteps leading to and fleeing from the crime scene.

That crucial piece of evidence was the work of Mark Sloan, Clay County GIS coordinator, who shares a busy office with four staff members on the third floor of the same courthouse building. Sloan spends most days scrutinizing the AutoCAD files he receives from architecture firms and updating property records and land parcels.

A fan of Robin Cook's suspense novels, Sloan welcomes the chance to help local law enforcement whenever he can. When "The District" was still airing on television, once in a while a police commander or a squad leader would call Sloan to ask if he and his staff could do what the fictional police chief Jack Mannion did using sophisticated GIS tools. (For more on that subject, see "Philadelphia Police Use GIS to Combat Crime.") Sloan could usually accommodate these requests, provided the resources he had were sufficient and the scenario was not something made possible by cinematic trickery. Generating high-resolution maps for detectives and tactical teams has become a part of his job.

Towering Evidence
Sloan has worked with county attorney Lisa Borgen before. He sometimes uses his expertise to prove that a drug-related crime has been committed within 300 feet of a school, for example, allowing the prosecutor to seek a heavier sentence under Minnesota law.

For the Mayhorn case, Borgen needed to first convince the grand jury, and later the trial jury, that the suspect and his associates traveled from Chicago to Moorhead to commit the crime. After she subpoenaed their cell phone records, she noted that several calls registered around the time of the murder. So she called Sloan and asked, "If we've got cell phone records, can you figure out where the calls were made from?"

"What I received was raw cell phone records," says Sloan. "I've never seen anything quite like that." Buried in the data were codes identifying each cell tower that transmitted each call. Cell towers are registered with the FCC and compiled into a searchable database, which proved a valuable resource for Sloan in this case. Using cell tower IDs, Sloan was able to query FCC's database and obtain the locations of the towers used.

Digging for Gold
As county GIS chief, Sloan had access to the data for Clay County but not for Chicago, across the state line from Moorhead, Minnesota. He had to hunt for the data he needed from several public sources; consequently, he had the unenviable task of consolidating the data that existed in various formats.

"Some were in lat/long (latitudes/longitudes), some in UTM (Universal Transverse Mercator), some in state-plane coordinates." To add to Sloan's headache, each state uses its own state-plane coordinate system. "In some cases, all we got were Shape files," he says. "Some came with metadata and projection files. For the ones that didn't, we had to use trial-and-error to figure out what projections they were based in. That can be a time-consuming process."

Eventually he was able to import his data into ESRI's ArcMap. When all the towers were charted, it became clear that whoever was on the phone had been traveling along the murderer's route.

Using cell phone records and cell tower locations,
Clay County GIS coordinator Mark Sloan was able to reconstruct
the route traveled by the suspect at the time of the murder.

It's Technology, Not Magic
"People think of GIS either as Big Brother or magic," says Sloan, who wants to debunk the myth. He's trying to promote it as a technology with a lot of potential, especially in judicial proceedings and crime fighting. It can, for instance, provide historic crime mapping, allowing police officers to study events over a period of time to identify trends. It can also play an important role in event planning, for early analysis of the exits, entry points and security vulnerabilities.

In this case, GIS helped put away Troy Mayhorn, a self-described "honest drug dealer."

When the trial was over, Sloan found himself at a reception for those who had worked on the case. "It was mostly law enforcement folks," Sloan recalls. Borgen presented Sloan with an honorary memento -- a gold-colored cell phone -- and a certificate inscribed, "In recognition of outstanding and dedicated service to the citizens of Clay County in the investigation and prosecution of the Nasean Jordan murder case."

Kenneth Wong is a former editor of Cadence magazine. He explores innovative use of technology and its implications in GIS Tech Trends and in Cadalyst magazine’s PLM Strategies column. Reach him at

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