Judge Gauvey, a magistrate judge on the United States District Court for the District of Maryland has issued a lengthy, thorough, and important decision on the use of cell phone data by law enforcement just to arrest someone. The opinion is available here (thank you Volokh conspirators for the link).
Here’s the juicy bit:
the government asks to use location data in a new way — not to collect evidence of a crime, but solely to locate a charged defendant. To some, this use would appear reasonable, even commendable and efficient. To others, this use of location data by law enforcement would appear chillingly invasive and unnecessary in the apprehension of defendants. In any event, there is no precedent for use of location data solely to apprehend a defendant in the absence of evidence of flight to avoid prosecution. The government did not submit, and the court did not find, any sufficient authority for this use of location technology. In light of legitimate privacy concerns and the absence of any emergency or extraordinary considerations here, the Court concludes that approval of use of location data for this purpose is best considered deliberately in the legislature, or in the appellate courts.