Wednesday, December 10, 2008

What does a GPS Unit Track? Proponent & Opponent

Imagine the situation: Your client is in interrogation, you (his attorney) by his side, law enforcement are asking questions nicely. Your client, sounding very reasonable, has explanations of his actions for the entire course of law enforcements time frame interest. Suddenly, they produce a map with a line on it, with little time stamps, which they tell you tracks the exact location of your client to the crime scene, and places him at the crime at the time it occurred! You look, and it seems to be what they are telling you. What do you tell your client?
First, if he looks as white as a sheet, you may be in trouble. However, if he's indignant, and maintains his innocence, look again at the sheet.
Many questions arise in such a situation. First, did the police actually have a GPS on your client's vehicle? Or person? Did your client have a GPS that evidence could be extracted from? Was the alleged crime the type law enforcement would have had either the warning (a tip) or the time (continuing investigation of one type or another) where a GPS could have been placed in advance? Is there any indication your client was under previous surveillance?
If the answers to all these questions are "no," you may have to consider that the "track" was constructed by the police to deceive your client into a confession. Remember, the police can lie.
How could they construct a credible deception? First, they probably know about the time the crime occurred. They probably know where your client lives, works, etc. Because GPS typically records all its data tracks in GMT (Greenwich Mean Time) rather than local time, both GPS units and programs to interpret the data from them "shift" their time data by a user selected number of hours (plus or minus GMT) to display the data in local time. Therefore:
  1. An officer can attempt to "recreate" a GPS track any time up to 24 hours (less the local adjustment) after the crime
  2. Then, the officer "fools" the GPS display software by giving it a false GMT offset number, and
  3. The officers print the resultant track and hand you something that looks like it took place both before, during and after the crime, and it has a real "feel" to it, as it is a real track, just "shifted" in time from the real crime timeline.
Its essential to remember that a GPS track shows where the GPS UNIT went, not necessarily where the person went, where the vehicle went, etc. To that end:
  • It is always essential to establish a foundation of 1) Who placed the GPS 2) when they placed the GPS 3) How they know the GPS was not disturbed, and (probably overlooked) 4) How does the court know that the GPS track offered came from this GPS, that is, who did the downloading, and how did they do it?
  • This offers plenty of defenses: What if the GPS was moved? What if a third-party moved a police attached GPS, committed the crime, and reattached it? How do we know who was driving the GPS-tracked vehicle, as GPS does not answer this.
  • I will later consider other defenses for an otherwise valid track, but don't forget them now.
Now, are potential counterfeit GPS tracks a reason to exclude AUTHENTIC GPS tracks? Absolutely not. However, courts and counsel must be sure to get the RAW, GMT data, with a chain of evidence, like burning from the GPS to a non-changeable read-only Compact Disk (CD-R), then do their own display of the data to ensure nothing inappropriate is going on.
Finally, if you get that raw data, get a display, check with an expert that it all looks right, the authentication steps are all there, and your client is still looking white as a sheet, it may be time to cut a deal - a valid GPS track is difficult to beat!

NEXT: Checking the "validated" GPS track

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