The Supreme Court on Wednesday ruled that the collection of GPS data by police without a warrant during an investigation into a man suspected of a string of thefts in the Kansai region was illegal.

The 15 members of the court's Grand Bench ruled that collecting data using a GPS invaded privacy and therefore constituted a mandatory investigation, which required a warrant.

But the court also raised doubts about whether an existing verification warrant could be used, underscoring that new legislation would be necessary to cover such GPS use.