Castillo v. United States of America

On October 28, 2025, the U.S. Supreme Court heard Castillo v. United States, a landmark digital privacy case. Elena Castillo was charged with wire fraud after the FBI obtained her private social media messages through a warrantless "geofence" reverse-location request to a tech company. The government argued that Castillo had no reasonable expectation of privacy in data shared with third parties under the third-party doctrine. Castillo contended that the sweeping nature of geofence warrants, which capture location data of countless innocent individuals, constitutes an unreasonable search under the Fourth Amendment. The case arose from an investigation into a cybercrime ring operating across state lines, but the evidence against Castillo was derived exclusively from the digital dragnet. The case highlighted tensions between traditional Fourth Amendment principles and modern surveillance technologies that generate comprehensive digital portraits of individuals without particularized suspicion.

In a 5-4 decision, the Supreme Court ruled that law enforcement must obtain a warrant based on probable cause before accessing geofence location data, holding that individuals retain a reasonable expectation of privacy in their comprehensive physical movements, even when incidentally collected by third-party platforms. Castillo's conviction was overturned, and the evidence suppressed.

Whether the warrantless collection of geofence location data from a third-party technology company violates the Fourth Amendment's protection against unreasonable searches and seizures, and whether the third-party doctrine should extend to non-volitionally shared digital location information.

The ruling redefined digital privacy rights for the modern era, compelling police to abandon warrantless geofence tactics used in thousands of investigations annually. Tech companies tightened data retention and access policies, while Congress began crafting bipartisan legislation to codify clear standards for emerging surveillance technologies, fundamentally altering the balance between law enforcement effectiveness and individual constitutional liberties.