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    Tracking Evidence with GPS Technology

    Recent cases nationwide and in Wisconsin recognize the power of Global Positioning Systems. With the increased accuracy of GPS technology, more lawyers are using -- and courts are admitting -- GPS evidence. Learn how GPS can affect your case.

    David Schumann

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    Wisconsin Lawyer
    Vol. 77, No. 5, May 2004

    Tracking Evidence with GPS Technology

    Recent cases nationwide and in Wisconsin recognize the power of Global Positioning Systems. With the increased accuracy of GPS technology, more lawyers are using -- and courts are admitting -- GPS evidence. Learn how GPS can affect your case.


    global positioning system by David A. Schumann

    In October 1999, William Jackson of Spokane County, Washington, claimed his daughter, Valiree, had been kidnapped on her way to school. Police suspected Jackson, but after searching his house and seizing his truck, they found no evidence. When Jackson's truck was returned, a detective told Jackson that police believed Jackson had buried Valiree's body in a shallow grave, that animals would dig it up, and that the body would be found and used to convict Jackson. Shortly thereafter, police seized Jackson's truck and recovered a GPS (global positioning system) tracking device that they had placed on the truck. The GPS track led police to three sites: a storage unit, an empty grave near a remote logging road, and a new grave miles away from the first grave, but only 50 feet from the tracked location. Confronted with the GPS evidence, Jackson admitted burying his daughter but denied killing her. He was tried, convicted of murder, and sentenced to 55 years in prison. Nearly all the evidence against him resulted from the GPS track and undeniably connected the body and its burial and reburial to Jackson. On appeal to the Washington Supreme Court, Jackson's conviction was affirmed because the police had used a search warrant.1 The court found that, without a warrant, the GPS track evidence would have been inadmissible under the Washington Constitution privacy clause, a clause much more restrictive than the U.S. Constitution's Fourth Amendment.2

    In 2002, Paul Seidler allegedly stalked his former girlfriend in violation of Wis. Stat. section 940.32(2)3 by use of a "Smart Track" GPS tracking device that he had placed under the hood of her car. The former girlfriend testified that she couldn't figure out how Seidler always seemed to know where she was; he followed her to work, on dates, and even to get gas. Police recovered the device's receipt and paper records of the former girlfriend's movements from L.A.S. Systems Inc., McHenry, Ill. The GPS transceiver used tracked vehicle movements and reported those movements by cell phone or computer via the Internet. Seidler pled no contest to stalking. The very GPS information that Seidler used to follow his former girlfriend supported the prosecution's case, impeaching any argument that Seidler's encounters were coincidental. "It was the cherry on the sundae," said Susan Karaskiewicz, Kenosha County assistant district attorney. "It was no longer a possibility of a 'he said-she said' case. In a way, the GPS provided the best witness."

    How a GPS Functions

    Global Positioning System (GPS) devices traditionally were used to navigate planes and ships, track shipments, and guide hunters, hikers, and anglers. GPS devices now are being used to track both possible victims and criminal suspects and to monitor people and things including convicted offenders, emergency vehicles, municipal vehicles, cell phone locations, media transport, and rental cars. GPS receivers can be smaller than a pack of cigarettes and cost as little as $89. Corporations and governmental bodies plan to use GPS information to do everything from setting insurance premiums to determining traffic patterns. GPS information will affect the legal rights of millions of people.

    GPS receivers produce an accurate progressive record of location and time, and can have the same persuasive courtroom clout as DNA evidence. However, GPS evidence may not always be accurate, relevant, probative, or otherwise admissible, because of how it is collected. This article explores the values and weaknesses of GPS evidence and suggests legal uses for GPS-generated evidence.4

    The Global Positioning System is a constellation of satellites that transmit timed coded pulses, like a radio tower transmitting radio pulses.5 Just as a phone is used to access the telephone system, or a radio to tune in radio signals, a GPS receiver is used to "tune into" the satellite pulses, process them with an onboard computer and a constantly updated quartz clock, and calculate a position fix. A GPS position "fix" consists of current longitude, current latitude, current altitude, and current time. Using an onboard computer, a GPS receiver monitors and updates this position fix, as often as once per second.6

    A GPS receiver can record a track, which is a series of periodically recorded fixes that are connected to form a line representing past travel. The GPS user also can save the current fix by pushing a button and marking a "waypoint," a named date-and-time-stamped fix that can be retrieved from memory at a later time. Waypoints can be strung together into a "route," which a GPS receiver can follow automatically.

    Tracks are a chronological transcript of travel, and waypoints are like time-stamped notes of events along the way. While both record histories, tracks are more or less automatically recorded, and waypoints take user effort and are easier to reference. Both are valuable as evidence.

    Simple GPS receivers do not transmit any radio or cellular signal, and are incapable of sending their location, even in an emergency. However, some GPS receivers are linked (in a single unit) with cellular or radio transmitters in what I call GPS transceivers (also called a "GPS tracking device"). Because a GPS transceiver emits a radio signal, FCC rules may regulate who may use a GPS transceiver.7

    GPS evidence faces increasing scrutiny under a State v. Jackson analysis and FCC regulation based on the method by which it was created. To summarize these principles: 1) Users can always track their own movements; 2) Users can usually track the movement of their own property, especially if the user/owner notifies any other drivers; 3) Tracks of third parties, or of their property, without their knowledge are probably inadmissible and even illegal, unless the tracks are conducted by law enforcement.8

    It is a good practice to consult an expert familiar with GPS and the law of the jurisdiction in which the user intends to track when there is a hazy situation. It also is good practice, when possible, to get written agreements and releases from anyone who could be tracked.

    Counsel will encounter GPS evidence: 1) created by his or her client for trial; 2) discovered from the other side (or third parties); and 3) created and offered by the other side in support of their case. When looking for GPS tracks,9 do not overlook General Motors' OnStar® and new GPS-enabled cell phones.10 A client or opponent may not know what a GPS receiver or a track is; they may only know that a rental car has a navigation system.11 Counsel's discovery questions should be simple yet comprehensive enough to elicit knowledge of the possible GPS systems installed.

    Although a typical GPS is accurate to 15 feet and two miles per hour of speed, tracks may not record all of this information. Just as digital cameras and sound recorders can be adjusted to take a higher resolution picture or higher quality audio, a GPS track can be adjusted to record position more frequently to give a higher quality graphical representation of position. Higher quality, though, means less time before the memory is filled and the data is written over. Legally, a low frequency track is like a fuzzy picture that may or may not help prove an issue, while a high frequency track is razor sharp, but may miss the critical event to be tracked.12 For instance, a low frequency track could show a client's location every 15 minutes and supply an alibi for a specific crime, while a high frequency track could show, second by second, that your client wasn't speeding when stopped.

    Most GPS tracks that are created will be erased whether intentionally or unintentionally. The memory in many GPS units is designed to hold only a fraction of the information that the GPS actually processes. Accordingly, a user must download GPS track and waypoint information, either by physical connection to a computer or with a GPS transceiver, a radio, or a cell phone connection. Even inexpensive commercially available software and a small personal computer can extract speed, exact position, distance traveled, and travel times, and can overlay the traveled track on maps or aerial photographs, which are available on the Internet. When saving data, be sure to use a program, such as G7toWin© (freeware), that downloads all track information before you use other programs to process the GPS data.

    Like a DNA readout, GPS evidence does not take sides. Counsel must detect its existence (or suggest its "capture"), analyze its worth, argue for or against its admission, and argue its persuasive weight with the finder of fact.

    GPS Evidence Admissibility

    GPS units track themselves, not an auto, person, or package. Any GPS track or waypoint admission requires a foundation showing what the unit was attached to, carried by, or contained in, together with the circumstances of its use. Track collection and preservation (such as downloading and burning to a CD) should be documented, and track correlation to maps and photos should be reviewed. Maps, for instance, actually may be less accurate than the track, and this discrepancy should be explained with the use of aerial photos. Any use of the track after downloading should be capable of re-creation by the opposition's expert.

    After downloading to a computer, tracks are no different than any other data file - they can be manipulated (like a sound recording), corrupted, or accidentally erased. Therefore, as soon as possible after creation, tracks should be downloaded and burned directly to a CD-ROM before correlation or further use. The persuasive power of the track is linked to the credibility of the person who created, downloaded, or correlated the track. When possible, a disinterested person should download and burn the track to a CD.

    Counsel must provide expert testimony to describe the GPS system, its accuracy, and its relevancy to the issue, unless the parties stipulate to these matters. Juries clearly do not have general knowledge of GPS systems. While GPS evidence may always be relevant under Wis. Stat. section 904.01, it may not always be probative. A low-frequency track with 15 minutes between trackpoints may show a vehicle's average speed of 35 m.p.h., but it will not show a defendant's 15 m.p.h. speed while obstructed by farm equipment or acceleration to 65 m.p.h. just before the accident.

    GPS tracks obtained without a warrant may be inadmissible because of constitutional considerations, such as those raised under the Washington Constitution in the Jackson case. However, to date there is no Fourth Amendment bar to GPS track evidence, and Wisconsin does not have a privacy clause similar to that of Washington.13 The U.S. Supreme Court allowed evidence gathered through a warrantless tracking device (a beeper) in an auto in United States v. Knotts,14 which involved tracking a chloroform container to a secluded Wisconsin cabin.

    GPS Uses in Specific Situations

    Most of the following uses represent the author's opinions on how GPS evidence can be used to assist practitioners. However, because GPS law is developing quickly, some of these methods already may have been used, but not reported, or reported too late to be included in this article. Check the case law and news sources before proceeding with these methods.

SchumannDavid A. Schumann, Marquette 1986, is a contract attorney practicing in Janesville, Wis.

    General Uses. GPS can be used to reinforce evidence previously dependent solely on witness credibility, such as attempts to serve process, and to establish jurisdiction when documents are served or when accidents occur. Often, two tracks can prove what one cannot. Two tracks that meet might show, for example, conspiracy, transfer of trade secrets, violation of probation conditions, or delivery of controlled substances. GPS waypoints can be used to mark sidewalk or road defects for statutory notice to municipalities or to quickly mark the location of evidence ejected from a moving vehicle. When time means life, emergency services may be liable if they do not use the available technology. Many emergency services are taking GPS "surveys" of their territories, marking waypoints for each address to guide emergency vehicles to rural driveways during driving rainstorms or in whiteout blizzard conditions. Surveyors use super-accurate sub-meter GPS receivers to get more accurate measurements - in inches - than other methods produce.15

    Even if a track itself might not be admissible primary evidence, it can lead to valuable secondary evidence. Tracks may jog a witness's memory, give clues as to a witness's location at a certain time, or lead to other evidence that confirms the track chronology. For instance, video surveillance cameras are everywhere these days - banks, convenience stores, gas stations, other businesses, and freeways. If the GPS track indicates passing one of these cameras in the critical time period, the videotapes' chronological reference may confirm the track chronology, and thus confirm an alibi or crime. Be sure to note differences between very accurate GPS time and potentially inaccurate VCR time and adjust the search accordingly. Other time-based systems, such as cell phone systems, can also help confirm a track. For example, a track and cell record might show a defendant was on the phone getting distracting news at the time of an accident.

    Criminal Law. Defendants charged with speeding may use GPS tracks, but cautiously - a track may show the defendant was not speeding when apprehended, but that he or she was speeding 20 minutes earlier. Accused citizens can use GPS tracks to establish alibi evidence to exonerate them of crimes. And, as in Jackson, GPS tracks can help locate other physical evidence. By following a GPS bearing, officers can serve warrants at the right address, in the dark, without excess warning to tip off the occupants.

    Law enforcement may use GPS movement "profiling" to follow a conspiracy without the conspirators' knowledge. For instance, an entire drug ring might be detected if officers attach a GPS to an informant's car and make a controlled buy. Officers could then watch the drug house and, having secured warrants, attach GPS units to other vehicles stopping there, then raid the drug house.16 Shortly thereafter, officers could recover the GPS units and see what possible new drug houses the patrons of the first house are using. The process unfolds in this second tier as it did in the first, and can be repeated multiple times. In each case, officers will look for short stops at residences or businesses with a lot of volume, and tracks from suspected drug buyers going to such houses. No one will be detained or questioned until the status of the residence as a drug house is established (with a controlled buy), and probably not until an entire ring is rounded up. GPS use conserves human resources and makes connections that otherwise would be difficult to prove. Furthermore, innocent citizens' lives are not disrupted in any way.

    Labor and Contract Law. Creative counsel can expand the range of situations in which GPS evidence can be legally gathered and admitted to court. A property owner will always have the right to monitor the location of his or her property, including vehicle fleets, trailers, containers, and equipment, but employment contract clauses may extend potential monitoring to employees in their private vehicles, or travels in cabs, or on public transit. Employee groups might "buy back" freedom from GPS monitoring at the cost of other benefits. Like drug tests, GPS monitoring could be random or focused, with proper cause. GPS information will disclose employee abuses, such as alcohol consumption while working, deviations from routes (useful in worker's compensation claims), reckless driving, and general shirking, and result in greater productivity. GPS tracks will prove when and where deliveries were made, how long employees are required to work, and how well they drive company or personal vehicles when the employer is liable for their driving. Businesses can contract for GPS proof of delivery before payment, thus shifting the record-keeping burden. GPS evidence can show a course of dealing under a contract (with repeated tracks), and show timely completion of terms or deliveries.

    Insurers will likely reward employers that monitor employees with lower rates, because GPS information will help predict and control risk, and confirm legitimate claims for early payment. With little effort GPS can document mileage deductions, trip costs, and hours for billing for delivery of time-based services, including legal fees.

    Family Court. Family court judges can order parties to use GPS receivers so that the court can monitor placement exchanges and end minor disputes that use major court resources. When one party has citizenship in a country that will not honor U.S. court orders or custodial decrees, a parent can monitor a child by using the new GPS bracelets or injected GPS implants, rather than deny an innocent parent physical placement periods simply because of parental citizenship.17 The same monitoring can reduce the risks of parental abduction, and speed location if abduction occurs.

    Under the right conditions, divorcing spouses who still live together but who are seeking child placement might legally track the movement of their own vehicles or their own children, and in so doing prove allegations of alcoholism or other problems that might affect the child's best interests. Tracking also might disclose hidden assets or contradict false testimony.


    GPS-related law is in its infancy, just as Internet law was in the mid-1990s. Careful counsel will preserve, use, discover, and, if necessary, create GPS evidence in support of a case, and effectively challenge opposing GPS evidence. Counsel who ignores GPS evidence will do so to his or her own detriment, if GPS evidence later shows counsel wasted an opportunity to clearly prove the case.


    1State v. Jackson, No. 72799-6, __ Wash. 2d __, __ P.3d __ (Sept. 11, 2003)

    2See infra n.13.

    32003 Assembly Bill 738 (introduced Jan. 7, 2004 and signed into law by Gov. Doyle on April 12, 2004) changes Wis. Stat. section 940.32 to include monitoring a victim by electronic means as part of a stalking "course of conduct" that an actor "knows or should have known" would cause the victim fear of bodily injury or serious emotional distress.

    4For an excellent source for all nonlegal aspects of GPS information, including operation, software, technical information, and links to other sites, visit http://gpsinformation.net/. For a good explanation of GPS history and some civil implications, see Comment, Global Positioning System (GPS): Defining The Legal Issues of Its Expanding Civil Use, 61 J. Air L. & Com 243 (1995). GPS receiver manufacturers sometimes post operating manuals for their products on the Internet for download, complete with features and abilities.

    5GPS should not be confused with two similar concepts, automobile "black boxes" and GIS (Geographic Information Systems). Auto black boxes use internal vehicle sensor information, such as speedometer readings and engine speed, and record it (in the black box) for later downloading. The information may be evidence of, for instance, vehicle speed before a crash. GIS systems are digital geographic models of the physical world, and may use many kinds of GPS data to determine where objects should go in the digital world. See Comment: The Legal Implications of Geographic Information Systems (GIS), 11 Alb. L.J. Sci. & Tech. 359 (2001).

    6For an in-depth look www.howstuffworks.com/gps3.htm.

    7For a listing of FCC regulations that may regulate GPS transceivers, see www.kapi.org/gps.html.

    8For an outline of the pitfalls of private use of GPS tracking on nonowned property, see www.kapi.org/gps.html.

    9In United States v. Rorke, 2003 U.S. Dist. LEXIS 16258 (E.D. Penn. 2002), the court noted that the government tracked drug suspects using OnStar that had been installed (presumably as standard equipment) on a rented vehicle. Similar tracking or records might be available for use in civil actions.

    10For general discussions of cell phone location technology, including GPS data, see Lost? The Government Knows Where You Are: Cellular Telephone Call Location Technology and the Expectation of Privacy, 10 Stan. L. & Pol'y Rev 103 (Fall 1998).

    11It is impossible to list all devices that currently have GPS capability and which of those devices have the capability to store GPS information for later extraction. Even if such a list was possible, today's cell phone model X might not have GPS capability and may look identical to tomorrow's model Y.

    12In the Laci Peterson murder case, GPS units recorded tracks very infrequently. This led to instances of admitted error, which the defense used as its main argument to exclude the GPS track evidence.

    13Wisconsin does have a privacy statute, Wis. Stat. section 895.50(2)(a), but it defines an "invasion of privacy" as an intrusion "in a place that a reasonable person would consider private or in a manner which is actionable for trespass." Because GPS rarely works anywhere but outdoors, an invasion of privacy as defined would only become an issue if GPS tracked movements on large tracts of private real estate, hidden from the public eye from both the ground and in the air. Article I, sec. 7, of the Washington Constitution provides that "(n)o person shall be disturbed in his private affairs, or his home invaded, without authority of law." This section conforms to section 652B of the Restatement (Second) of Torts: "One who intentionally intrudes, physically or otherwise, upon the solitude or seclusion of another or his private affairs or concerns, is subject to the other for invasion of his privacy, if the intrusion would be highly offensive to a reasonable person." However, Wis. Stat. section 895.50 does not follow the Restatement: "However, the legislature did not use the phrase 'solitude or seclusion of another or his private affairs or concerns' to describe the area of invasion under sec. 895.50(2)(a), Stats., but, rather, 'a place.'" Hillman v. Columbia County, 164 Wis. 2d 376, 392, 474 N.W.2d 913 (Ct. App. 1991). Therefore, collecting GPS data in public places would not violate Wisconsin's privacy law. "Nor can one complain when publicity is given to matters which a person leaves open to the public eye. The law is not for the protection of the hypersensitive, and all of us must to some extent lead lives exposed to the public gaze." Prosser and Keeton on Torts, § 117 at 857 (5th ed. 1984), cited in Zinda v. Louisiana Pacific Corp., 149 Wis. 2d 913, 930, 440 N.W.2d 548 (1989). See generally Note: Satellite Tracking and the Right to Privacy, 53 Hastings L.J. 549 (2002). Placing the GPS device might constitute a "trespass" on the vehicle, but see U.S. v. McIver, 993 F. Supp. 794, 798 (1998) (evidence suppressed on other grounds) (approving placement of GPS tracker and BirdDog beeper under a truck bumper in private driveway outside the curtilage of home.) Under Wis. Stat. section 968.27(4)(d), Wisconsin also excludes "any communication from a tracking device" from its definition of "electronic communication" as that term is used in Wis. Stat. section 968.31 ("Interception and disclosure of wire, electronic or oral communications prohibited.") GPS transceiver tracking, therefore, is not wiretapping.

    14460 U.S. 276 (1983).

    15Super-accurate GPS measurements require a several-thousand-dollar GPS receiver to be placed motionless on a tripod over the spot to be measured for anywhere from minutes to hours, and may require subsequent computer processing of the raw data.

    16For probable cause, it may be necessary to quietly arrest the dealer, and make a deal for leniency in exchange for names or descriptions of autos for GPS warrants for the dealer's customers, then allow the dealer to continue business long enough to attach the devices to the customers' vehicles.

    17Long v. Long, 2001 WI App 46, 241 Wis. 2d 498, 624 N.W.2d 405, demonstrates the problem facing the court, although no GPS tracking was ordered in that case.