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Court decisions have been split on the legality of police using GPS devices to track the movements of suspects without a court warrant. Currently there are no laws that regulate the use of the Global Positioning System in criminal investigations. A 2006 National Police Agency directive tells police forces nationwide they can use the devices when urgent action on a crime is required and other means of trailing the suspects aren’t feasible. But the Nagoya High Court judged in June that the warrantless use of such devices to investigate a serial theft case was illegal because it violated the suspect’s privacy.

The high court went on to warn that the threat to the privacy of people under criminal investigation from the use of GPS devices will increase with further advances in the technology — and called for new legislative action to resolve the problem. Relevant parties should take the warning seriously and start discussing legal controls on the use of GPS in investigations.

GPS is indeed a useful tool for police investigators. The police rely on the positioning service provided by a major security firm using the GPS system. Investigators secretly attach a rented device to the underside of suspects’ vehicles. They can then monitor their locations on a map by accessing the security firm’s server with their cellphones.

The NPA directive, however, does not require investigators to get a court warrant to use GPS. Unlike the wiretapping of telecommunications, whose use in investigations is restricted to certain types of crimes and based on warrants, there are no statistics available on how the GPS devices are being used in criminal probes. In court cases in which the legality of the use of GPS was contested, prosecutors have argued that such devices are used by investigators only as supplementary tools to their trailing and staking out of suspects, whereas the defense side claimed that the use of GPS infringed on their clients’ privacy.

Court decisions on the issue have varied. In June last year, the Osaka High Court determined that Osaka Prefectural Police acted illegally when investigators put GPS devices on more than a dozen vehicles used by a suspect and his associates in the probe of a 2013 theft. Noting that the warrantless use of the GPS devices over an extended period gravely violated the privacy of the accused, the court refused to accept evidence obtained through use of the devices, although it found the man guilty nonetheless on the basis of his guilty plea. But in the appellate trial, the Osaka High Court determined that mere information about a suspect’s location does not reveal his concrete behavior and cannot be deemed to constitute a serious breach of privacy.

The Nagoya High Court decision in June involved a different theft case, in which the Aichi Prefectural Police attached GPS devices on the defendant’s car for 3½ months in 2013 and determined its location more than 1,600 times. The use of GPS in the probe can hardly be called a supplementary tool. While upholding the lower court’s guilty verdict on the grounds that it was based on evidence obtained through other means, the high court said the use of GPS in this case was illegal — and ruled that the risk of privacy violations inherent in GPS-based probes “materialized to a substantial degree.”

The GPS system, the high court said, gives investigators constant access to fairly accurate information about the suspect’s location over an extended period. Analysis of the GPS data can comprehensively reveal information about suspects, including their personal acquaintances, thoughts and beliefs as well as tastes, the court said, noting that the risk of privacy infringement will rise further if precision of GPS data rises with advances in the technology and enables more detailed and easy tracking.

The court’s warning is worth heeding, given that the issue of maintaining the privacy of people under criminal investigation will not be easily reconciled. At least the rules must be clarified and made transparent in the use of investigation tools that potentially clash with people’s privacy rights. While the scope of wiretapping in criminal probes is being expanded, investigators are required by law to report to the Diet the number and duration of such probes. There seems to be no reason that similar procedures should not be required in the use of GPS in investigations.

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