Friday, May 29, 2009

GPS Evidence Q & A

Thanks to "D" for the following questions, which I will answer subject to the disclaimers on the bottom of this page, and as hypothetical situations:

Question 1:
Does the GPS receiver have to be 'sealed' or at least in official custody to prevent tampering (upload of bogus track) when used to track a suspect or gather evidence for conviction?

A: Laws vary from jurisdiction to jurisdiction, and new laws are being enacted every day. Accordingly, that would depend on both the rules of evidence in the particular jurisdiction, and on the judge the GPS track evidence was presented to for admission. If there are no statutory requirements, generally all evidence must be accounted for in a "chain of evidence." In short, this would require those who attached the GPS and collected to swear to the manner of secure clearing of the GPS unit, the manner of GPS evidence retrieval (that is, was the entire GPS recovered, or was it downloaded by phone or by close proximity secure download.) Furthermore, the officers would have to testify regarding how the GPS track sought to be entered into evidence was securely stored, then about how it was processed for display to the court or jury. I've said this before- because a GPS track is just a data file, the information it contains is only as valuable as the veracity of those swearing to it. While GPS evidence is a particular type of evidence, it is, short of a jurisdictional control, just evidence. The proffered GPS track does have to be relevant to the situation in court, and not just a "Gee, Judge, we want to wow the jury with our CSI-like abilities, even though our GPS track has nothing to do with the case we are trying. . ." Law enforcement may choose to "seal" both the GPS and any downloads of GPS to make the job of introducing the GPS track into evidence easier, but it is not required. See my blog entry on relevancy here

Of course, in Washington, Oregon, and now New York, a warrant is required to even attach the GPS to the suspect or witnesses car. I will discuss the New York case (and Wisconsin's appeal court decision that did not require a warrant for GPS tracking in a blog shortly.

Question 2:
How can a receiver be used as defense (e.g. speeding) if it wasn't taken as evidence
(I could upload more bogus track info)?

A: Again, I take this as a hypothetical. See question 1, above, that all GPS data is only as credible as the person attempting to admit it. Given that a suspect of speeding suddenly has a GPS track of himself not speeding, which he did not disclose to the officer at the scene would be highly suspect. Why did this hypothetical suspect not disclose the supposedly exonerating GPS track to the arresting (or ticketing) officer? Simple-the suspect thought it might prove he was speeding! He wanted to check it out first. If he confirms he was, then he'll likely pay the ticket.

Likely, because the suspect doesn't know how to 1) preserve the track and 2) show the track in a manner the court might find acceptable, it is unlikely a court would admit such a track after the fact. The one exception I could see-where the track is both gathered and kept by a third party, that is, a remote tracking service that has no stake in the case, no reason to lie, and a business interest in keeping accurate records. Such records would be both tamper-proof (or at least resistant) and credible. The remaining qualification-would the GPS track of a speeding suspect be relevant? See my above link on relevancy, which is highly applicable to speeding situations. In short, because GPS tracks average speeds between track log points, only an extremely "dense" track (with a lot of track points, recorded very frequently, on the order of one track point a second or every two seconds) would have the accuracy to overcome a police radar reading that, at a particular point the radar gun was pointed at the suspect, he or she was speeding.

So, hypothetically, could a suspect after the fact tamper with a track, or create a track and load it into a GPS for police consumption? I've suggested in blog posts police could "dummy-up" a track to present to a suspect. Why shouldn't a suspect do this?

Two huge reasons:
1) Police are allowed to lie, suspects are not. Police are allowed to fabricate evidence to challenge a suspect's declarations of innocence to test his story. An innocent suspect, goes the theory, will stick to his story no matter how much false evidence is before him. A guilty suspect will confess because he thinks he's been caught.

Suspects, however, are not allowed to lie to the police, or present false evidence. Its a crime in most jurisdictions, called "Obstruction of Justice" or something of the like. Uploading a "bogus" GPS track and presenting it as real or tampering with a real track is either perjury or obstruction of justice, or both. Both are very serious, not like a speeding ticket.

2) A suspect in an interrogation room won't have time or expertise to analyze police evidence put before him or her, but police will have all the time in the world to analyze GPS evidence offered by a defendant to a speeding charge. Any offered track would be, at the least, part of the police file, at most, part of the court's evidence, and would stay in the file for analysis (today, or by future, more sophisticated methods) for years.

Police Experts (and private experts) can detect "bogus" tracks, given enough time. I won't get into all the ways, but one way is the laws of physics and common sense. For instance, if a track shows someone proceeding at 60 mph but slowing so suddenly that skid marks would have to be produced to do so, (and there are no skid marks) it would be evident that a track had been tampered with. Track points are time stamped, and tiny differences make huge differences in speed. Since one track point is dependent on the previous track point position, and so on, a tampering suspect might try to show he wasn't speeding for on stretch of road, but show he was speeding two minutes earlier. This internal structure of GPS tracks helps enhance their credibility and decreases the chance tampering won't be found.

Obstruction of justice is likely a much more serious offense than speeding, and not only would a court be likely to "throw the book" at a speeder who tried to fake a GPS track on the speeding charge, he or she would also likely throw the book at the speeder for obstruction of justice.

Thanks, "D" for raising this hypothetical question.

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