Policing by Numbers: Big Data and the Fourth Amendment

INTRODUCTIONThe age of "big data" has come to policing. In Chicago, police officers are paying particular attention to members of a "heat list": those identified by a risk analysis as most likely to be involved in future violence.1 In Charlotte, North Carolina, the police have compiled foreclosure data to generate a map of high-risk areas that are likely to be hit by crime.2 In New York City, the N.Y.P.D. has partnered with Microsoft to employ a "Domain Awareness System" that collects and links information from sources like CCTVs, license plate readers, radiation sensors, and informational databases.3 In Santa Cruz, California, the police have reported a dramatic reduction in burglaries after relying upon computer algorithms that predict where new burglaries are likely to occur.4 The Department of Homeland Security has applied computer analytics to Twitter feeds to find words like "pipe bomb," "plume," and "listeria."5Big data has begun to transform government in fields as diverse as public health, transportation management, and scientific research.6 The analysis of what were once unimaginable quantities of digitized data is likely to introduce dramatic changes to a profession which, as late as 1900, involved little more than an able-bodied man who was given a hickory club, a whistle, and a key to a call box.7 Real-time access to and analysis of vast quantities of information found in criminal records, police databases, and surveillance data may alter policing8 in the same way that big data has revolutionized areas as diverse as presidential elections,9 internet commerce,10 and language translation.11 Some have even heralded big data's potential to change our assumptions about social relationships, government, scientific study, and even knowledge itself.12In the private sector, retailers have harnessed big data to produce some seemingly trivial but surprising changes to their practices.13 A much discussed example stems from Target's extensive use of data analytics to identify certain purchases, such as supplements commonly taken during pregnancy, to know whether a customer is pregnant, without the woman disclosing the pregnancy herself.14 For a retailer, pregnancy is a prime opportunity to target a consumer when shopping habits change and expand. An irate father allegedly complained to Target that his daughter was unfairly targeted as a pregnant woman with coupons only to discover, to his chagrin, that Target was better informed than he was.15 Similarly, Walmart, through its computerized retail tracking, has discovered that Strawberry Pop-Tarts and beer sell as briskly as flashlights when hurricanes are forecast. These products were quickly shipped to Florida Walmart stores in the path of Hurricane Frances in 2004.16Yet unlike the data crunching performed by Target, Walmart, or Amazon, the introduction of big data to police work raises new and significant challenges to the regulatory framework that governs conventional policing. From one perspective, the Fourth Amendment has proven remarkably flexible over time. Constitutional law has governed ordinary policing whether the crimes involved bootlegging, 17 numbers running, marijuana farming, or cell phones. As the sophistication of criminals has increased, so too have the tools of the police. In the twentieth century, perhaps no two tools have been as revolutionary to modern policing as the two way radio and the patrol car.21In this century, big data-in a variety of forms-may bring the next dramatic change to police investigations. One researcher has concluded that it will soon be technologically possible and affordable for government to record everything anyone says or does.22 How well will the Fourth Amendment's rules pertaining to unreasonable searches and seizures adapt to the uses of big data? Scholars have widely discussed the shortcomings of applying Fourth Amendment doctrines, once adequate for a world of electronic beepers, physical wiretaps, and binocular surveillance, to rapidly changing technologies. …