The Court of Justice of the European Union (EU) ruled on Tuesday that national governments cannot allow the “general and indiscriminate retention” of traffic and location data from electronic communications. The court’s ruling stems from a long procedural history. In 2015, an Irish court convicted Graham Dwyer of the 2012 murder of Elaine O’Hara. Dwyer appealed to the Irish Court of Appeal, arguing that traffic and location data from his phone calls were improperly admitted into evidence. at trial. Dwyer separately brought a civil action in the High Court of Ireland challenging a 2011 Irish data law on the grounds that it breached EU law. The High Court ruled in Dwyer’s favour, and prosecutors appealed to the High Court of Ireland. The High Court of Ireland then referred the matter to the Court of Justice. The court concluded that established EU law “enshrines” a guiding principle that prohibits the retention of traffic and location data from electronic communications. This principle is part of the fundamental right of EU citizens to “respect for private life and protection of personal data”. The court members acknowledged that, based on previous case law, member state legislatures may allow limited data storage in specific cases. for “the purposes of combating serious crimes and preventing serious threats to public safety.” These limited exceptions include: targeted retention of location and traffic data that is limited, based on the categories of individuals involved or using a geographic criteria; the general and indiscriminate retention of IP addresses assigned to the source of an Internet connection; the general and indiscriminate retention of data related to the civil identity of users of electronic communications systems; and expedited retention (flash freezing) of traffic and location data held by those service providers. The exact effect of the court’s ruling on Dwyer’s case is unclear. In a statement, Irish Justice Minister Helen McEntee said: “[t]The case will now return to the Supreme Court and the Department of Justice will consider, along with the Attorney General’s Office, the Supreme Court’s ruling when the case is finalized.”