ANNAPOLIS – Saying everyone knows what a GPS does, Maryland’s top court has ruled that an expert did not need to testify about the tracking device at the trial of a state transit police officer who was convicted of assault and misconduct in office.
In its 5-2 decision, the Court of Appeals rejected Martaz Johnson’s argument — through the state public defender’s office — that the data placing him at the victim’s home should have been excluded as evidence at trial because the prosecution failed to call an expert to explain the Global Positioning System technology to the jury.
Such expert testimony is not necessary because “GPS technology is pervasive and generally reliable,” the court said Wednesday.
“Although a user may not understand precisely how a GPS device works, the same is true for other commonly used devices such as clocks, scales, and thermometers,” Judge Robert N. McDonald wrote for the majority.
“The general public has a common-sense understanding of what information the device conveys – time, weight, temperature – and of the margin of error to which such devices are ordinarily subject: a colleague’s watch may tell time a minute faster or slower than one’s own; the scale at the gym may display a different weight than the scale at home; and a thermometer that estimates child’s temperature may give a slightly different answer in a second reading,” McDonald added. “In the same way, the general public relies on GPS devices to locate a destination, to ascertain a route to get there from a current location, and to estimate the duration of travel.”
The Maryland attorney general’s office praised the court’s decision in a statement Friday.
“We think the Court of Appeals was correct in recognizing that the common experience of jurors evolve over time, and that most jurors today use and understand GPS technology,” the office stated. “There is no longer a need for an expert witness to explain these types of records.”
The Maryland public defender’s office did not respond to a request for comment.
At the trial, a police sergeant testified that a GPS device in Johnson’s Maryland Transit Administration patrol cruiser revealed that he spent 37 minutes near the Baltimore home of a woman he had driven home and allegedly attacked after her car was struck by an MTA bus the prior evening. The Baltimore City Circuit Court jury, having heard no expert testimony on the GPS device, acquitted Johnson of rape and burglary but found him guilty of misconduct and two counts of second-degree assault in the March 13, 2014, incident.
The Court of Special Appeals affirmed the conviction in an unreported opinion last December, prompting Johnson’s appeal to the high court based on the absence of an expert explanation of GPS technology.
In its decision, the Court of Appeals distinguished GPS data from DNA evidence, which, though well known, requires an expert to explain at trial.
“Although we use acronyms to describe both types of evidence and both are the product of scientific advances, the comparison is superficial,” McDonald wrote.
“An average juror may have some familiarity with the science and technology underlying DNA analysis from a high-school science class or a television show, but jurors do not use DNA analysis in their daily lives,” McDonald added. “The average lay juror has little experience on which to evaluate the information conveyed by DNA analysis and little sense of the margin of error associated with such analysis.”
The high court said defense counsel remains free to cross-examine the state’s witness about defects in the GPS data or to present expert testimony challenging the device’s accuracy.
McDonald was joined in the ruling by Chief Judge Mary Ellen Barbera and Judges Clayton Greene Jr., Michele D. Hotten and Joseph M. Getty.
In dissent, Judge Shirley M. Watts agreed that “routine GPS information” about travel is well-known and need not be explained by an expert witness. However, the tracking information cited at Johnson’s trial included data regarding the duration of his stops, which goes beyond the public’s general use of the technology and requires expert testimony, added Watts, who was joined in dissent by Judge Sally D. Adkins.
The Court of Appeals rendered its decision in Martaz Johnson v. State of Maryland, No. 6, September 2017.