Over the last few years, the debate over whether a person is entitled to his or her privacy while in public has taken a fervent — and at times, disjointed — path. Since March, Minnesota, Missouri, Illinois, New Hampshire, Tennessee and South Carolina have moved forward with legislation banning warrantless cellphone tracking. These states joined Maine and Montana in outlawing warrantless cellphone surveillance, and New Jersey, where the state supreme court ruled that it was unconstitutional for law enforcement to surveil without probable cause.
At roughly the same time, the American Civil Liberties Union revealed that a number of police departments in Florida have entered into confidentiality agreements allowing the use of “stingrays” — mobile false cellphone antennas that trick mobile phones into revealing their locations — in undercover investigations.
Even in the courts, the question of warrantless cellphone tracking has yet to be answered with any definity. In July 2013, the U.S. Court of Appeals for the 5th Circuit overturned a Houston federal judge’s ruling stating that cellphone data is constitutionally protected and can only be acquired with a search warrant. Four months later, however, the 3rd Circuit ruled in the case of the United States v. Katzin that law enforcement officers must have a valid warrant to install a GPS tracker on a suspect’s vehicle, saying such a search was unreasonable.
In question with all of these cases is the interpretation of the Fourth Amendment guarantee against unreasonable search and seizure. For those who argue that law enforcement has the right to surveil a person in public without a warrant, there is the assumption that once a person is outside the confines of his or her private space, expectations of privacy become invalid. In other words, a person in a public space is a public entity, free to be observed and surveilled by those who have a public safety obligation to do so.
Researchers at the University of Maryland Francis King Carey School of Law and Columbia University’s Department of Computer Science, however, beg to differ. In an article published in the New York University Journal of Law & Liberty, the researchers argue that advances in computer science and the proliferation of monitoring devices throughout the public space create a situation in which a person can theoretically be tracked from the moment he or she leaves home to the moment he or she returns.
This concept, known as mosaic theory, is based on an assumption in intelligence-gathering that while a single item, such as a cellphone ping indicating that a person visited a certain store at a certain time, does not say much about a person’s habits or interests, many items, when looked at from the same point-of-view, may reveal the defining habits and tendencies that constitute the person. Building this “mosaic” of information would make it increasingly possible to make predictions about the target.
While each of the individual surveillance items, in and of themselves, may constitute a reasonable search, the analysis of the sum of a continued cycle of such surveillance without a warrant can be argued as a violation of the Fourth Amendment.
“The sequence of a person’s movements can reveal still more; a single trip to a gynecologist’s office tells little about a woman, but that trip followed a few weeks later by a visit to a baby supply store tells a different story,” ruled the U.S. Court of Appeals for the D.C. Circuit in 2009. “A person who knows all of another’s travels can deduce whether he is a weekly church goer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups — and not just one such fact about a person, but all such facts.”
As information gathered by surveillance devices in a region tend to be collected by a single computer or by a network of computers, and as advances in computer science have made data analysis quicker and cheaper, the researchers agree that the collection of “breadcrumbs” that come from warrantless electronic surveillance can be tested toward proving if a mosaic exists — which would violate the privacy of the individual.
“At least in principle, machine learning lets us answer one of the key challenges posed by the mosaic theory: how to tell if a mosaic exists,” wrote the researchers. “In his piece on the mosaic theory, Fourth Amendment scholar Orin Kerr notes the three different expectation of privacy theories for prolonged location tracking in the opinions by Justice Alito (‘a degree of intrusion that a reasonable person would not have anticipated’), Justice Sotomayor (‘a manner that enables the Government to ascertain, more or less at will, their political and religious beliefs, sexual habits, and so on’), and Judge Ginsburg (‘the likelihood a stranger would observe all . . . movements [of a person over the course of a month] is not just remote, it is essentially nil’).”
As technology improves, the potential that it can be used to violate civil liberties also grows. According to Renee Hutchins, a researcher that participated in the paper, the key is understanding this potential and taking steps to accommodate it.
“The answer will only come when the two disciplines begin working together. It’s essential that the legal and computer science communities work together, and that the law on location tracking continues to keep step with the current state of scientific discovery,” Hutchins told Inside Counsel.