Mass Data Search Warrants and the Constitution

In our data-saturated times, the key evidence in a criminal case often is digital. As investigators deploy new tools such as keyword and geofence warrants to follow technological trails, courts and commentators are split over the constitutionality of such tactics. A keyword warrant asks search engine companies to reveal users who searched incriminating keywords before a crime. A geofence warrant asks technology companies to search vast troves of user location data for persons present around the time and place of a crime. Penned in an era before electrical power, much less vast privately held digital databanks, the Constitution’s text is hard-stretched to apply to modern mass data searches. Courts vary dramatically. Some courts hold that the Fourth Amendment does not apply at all to data that we reveal to a third party, such as Google. Other courts hold that geofence and keyword warrants are modern-day general warrants prohibited by the Fourth Amendment. Some courts avoid the thorny constitutional question by ruling that in any event, good-faith reliance on a warrant signed by a magistrate judge precludes exclusion of evidence. This article forges a middle path between the extremes to evaluate the sufficiency of modern-day mass data search warrants. The article frames the concepts of digital probable cause and particularization, updating the Fourth Amendment for data searches. Digital probable cause is based on a fair probability that evidence of a discrete known crime will be found using data search parameters. Digital particularization refers to particularization via parameters such as the time, place, and circumstances of a crime, including likely keywords a perpetrator would use to plan it. Modern data searches must be specifically tailored to uncover evidence of a discrete known crime with time, place, and geographical or likely keyword parameters to limit roving searches. In contrast, roving digital hunts for a crime, such as searching for people who googled keywords like “abortion” in a state that criminalizes abortions, would fail to satisfy probable cause and particularization requirements. Any such modern-day general warrant authorizing digital rummaging untethered to the specific details of a known offense would patently violate the Fourth Amendment.