Today brings a welcome ruling in Commonwealth v. Augustine: people may have a reasonable expectation of privacy in their historical cell location information data and prosecutors may need a warrant based on probable cause – and not just a 2703(d) order under ECPA – to obtain it. The opinion relies on Art. 14 of the Massachusetts constitution and not the Fourth Amendment, but hey, I’ll take it.
Orin Kerr writes:
The Massachusetts Supreme Judicial Court has issued a new decision interpreting the Massachusetts constitution to require a search warrant for access to a two-week span of historical cell-site information. The court divided by a vote of 5-2. Note that the decision did not interpret the Fourth Amendment of the federal constitution, but rather interpreted Article 14 of the Massachusetts Declaration of Rights. This means that the decision is binding on Massachusetts state law enforcement, but it does not apply to federal law enforcement (whether in Massachusetts or outside it).
The decision appears to adopt a mosaic theory for the state constitution, by which the time of surveillance determines what is a state-constitution search.
Read more on WaPo Volokh Conspiracy.