Wednesday, February 18, 2009

GPS Evidence Repository?

We are now entering the age where GPS tracking information, that is, GPS evidence, is collected on numerous people on a routine basis. We also live in an age where it is easy to keep 1) who (or what vehicle) the GPS track is related to 2) the raw data (which at the least consists of time, longitude and latitude, with some tracks adding altitude).

Whether such information is collected by an employer, a third party working for an employer, or as part of an investigation, clearly there will be evidentiary information related to such a "storehouse" of information. Now is time time to start programs to collect and preserve it.

Imagine an unsolved murder of a young suburban woman at her home. No clues exist to tell who killed her. However, someone using a GPS evidence repository (like a fingerprint or DNA repository) can chart the location of the murder, and look for all tracks that would have passed, for instance, within 200 feet of the murder site for a specific period of time, like three weeks before the murder. If this produces too many tracks, the search can be limited, either by distance or time period. While this does not mean additional tracks will not be followed up on, just filtered to get the most closely related tracks first.

Now imagine the detective in charge of the case has run this check, and found a UPS truck that stopped across the street, and a car stopped near the victim's residence that was tagged as going to a drug house (using the investigative technique I set forth in my Wisconsin Lawyer article). Correlations to know evidence are checked, and the detective discovers the vehicle is owned by an individual who showed up on caller ID at the victim's home, and who admitted a social relationship to the victim, but denied seeing the victim on the day of the murder. Further examination of the UPS truck & target car tracks shows that, although not in exact area of the murder at the same time, the target car passed the UPS truck at excessive speed shortly after the murder. The target car is photographed and the UPS driver remembers both the delivery and that the target car almost sideswiped him at high speed. This identification gives enough evidence to get a search warrant for the vehicle (which the police find easily with real-time tracking as the GPS is still attached.) A few pieces of physical evidence are found in the vehicle, but following the GPS track backward, the police find the target vehicle went to a pawnshop. At the pawnshop, the owner finds items from the victim's home, and picks the suspect from a lineup. The suspect is arrested, and confesses he attempted to enter the woman's home to steal items for drugs, but was surprised by her and killed her to avoid detection.

This little tale (totally fictional) demonstrates how a GPS evidence repository made up of both routine commercial records and law enforcement GPS evidence can be a valuable investigation tool. Today, we are building biometric and electronic repositories, including phone records, international travel records, immigration records, billing records and the like. Most can be retrieved and cross referenced to build cases and serve justice. Why not GPS tracking records?

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In a related subject, given a known vehicle but an unidentified driver, is there a way of telling whether the vehicle was driven by a specific person? I think there is. Driving habits, as shown by GPS records. I call it GPS profiling. We all drive differently, and our routes at a given time, our acceleration, our stopping practices and our following practices all differ. Now, our driving may not be so different as to pick one driver from the general population, but driving probably varies enough (given a known baseline, that is, several different incidents of driving compared to one questioned incident) to be able to pick out one individual from say, for example, four or five people who actually had access to a vehicle and opportunity to drive it.

Of course, GPS profiling doesn't discriminate, that is, it looks at the movement of the vehicle as controlled by the driver, in order to tell who that driver is. There are several items necessary to draw any conclusions from a GPS evidence put into a profile:
  1. Exemplar GPS tracks, like the writing samples a handwriting expert needs to judge against a questioned writing. These exemplars would have to be from any person that was suspected of driving during the questioned track.
  2. A high resolution GPS track-Just as a handwriting expert can't make conclusions based on fuzzy copies or blurred signatures, or a photo analyst can't make a conclusion based on blurry photos, a GPS expert would have to have sufficient track points, showing time and location, to actually make a conclusion about driving patterns. As a rule, I would say anything that is beyond 5 or 6 seconds track points would be of doubtful use for GPS profiling, because profiling would require reading subtle differences in driving style. This does NOT mean track points beyond 5-6 seconds aren't accurate and valuable for other types of analysis or evidentiary use, just that they wouldn't be much use for telling who was driving the vehicle based on prior GPS track incidents.

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