Robert Galbraith / Reuters

In her solo dissent from a case at the U.S. Supreme Court on Monday, Justice Sonia Sotomayor chose to be blunt about the ruling's implications. “By sanctioning a ‘shoot first, think later’ approach to policing, the Court renders the protections of the Fourth Amendment hollow,” she wrote of her colleagues’ 8-1 decision in Mullenix v. Lena to shield a police officer from liability for shooting a man during a high-speed chase.

Mullenix is neither a high-profile case on the Court’s docket nor a landmark decision in its jurisprudence. But Sotomayor’s dissent from it adds to what has become an increasingly prominent theme of her tenure: the Fourth Amendment’s constraints on law enforcement, and a skepticism toward those who try to stretch them.

This particular case centered on the death of Israel Leija, Jr., who was shot and killed by Chadrin Mullenix, a trooper with the Texas Department of Public Safety, during a high-speed pursuit on Interstate 27 near Tulia, Texas, in 2010. The chase began when a local police officer attempted to arrest Leija on an outstanding warrant in Tulia. Leija fled, leading officers on an 18-minute, high-speed pursuit. During the chase, Leija called the local police dispatcher and, in what the dispatcher interpreted as a state of intoxication, warned that he had a gun and would shoot officers pursuing him.

DPS officers set up spike strips, designed to puncture a fleeing suspect’s car during a high-speed chase, along Leija's route. Mullenix set his up near an overpass further down the interstate. He then radioed one of the pursuing officers and proposed trying to shoot Leija’s car to disable it, which he had not been trained to do. The other officer told him to “stand by” and “wait to see if the spike strips work.” Leija’s family claims Mullenix heard this response; Mullenix denies it. Mullenix then took out his service rifle, waited on the overpass for Leija to arrive a few minutes later, and fired six shots at the vehicle as it passed under him toward the spike strips. Four of the shots struck Leija, killing him.

Leija’s family subsequently sued Mullenix, arguing the officer’s excessive use of force violated Leija’s Fourth Amendment rights. Lower courts agreed and waived Mullenix’s qualified immunity, which protects police officers from legal liability unless they violate clearly established constitutional rights. But in an 8-1 decision, the Supreme Court ruled Mullenix was indeed protected by it in this case because the inappropriateness of his actions had not been sufficiently established under existing precedents.

The Court decided the case per curiam, meaning “from the bench,” with no oral arguments and no individual name attached to the opinion. Only Sotomayor dissented from the Court’s consensus, though Justice Antonin Scalia filed a brief, separate concurrence in which he distinguished between the “use of
force that happens to kill the arrestee” and the “application of deadly force.”

First, Sotomayor wrote that Mullenix failed to prove shooting Leija was necessary when the spike strikes would have stopped his car and ended the pursuit without lethal force. Accordingly, she then alleges the majority “glossed over the facts” of the case and wrongly focused on the decision to stop the car instead of the manner in which Mullenix did it. Finally, she notes Mullenix’s first words to his superior officer after killing Leija were, “How’s that for being more proactive?” He was apparently referencing another officer’s critique during a counseling session; Sotomayor said the remark reflected “the culture this Court’s decision supports” when it shields an officer who used deadly force “for no discernable gain and over a supervisor’s express order to ‘stand by.’”

Sotomayor’s concerns about the Fourth Amendment long precede this case. One of the earliest and most significant examples came in the 2012 case United States v. Jones. In that case, federal agents clandestinely attached a GPS tracking device to the car of Antoine Jones, a Washington, D.C., nightclub owner, without a valid warrant and monitored his movements for a month. Federal prosecutors then used the information obtained from their surveillance to convict Jones of narcotics trafficking, for which he received a life sentence. Jones challenged his conviction by arguing the warrantless monitoring of his movements violated the Fourth Amendment.

The Court unanimously ruled that placing warrantless GPS tracking devices on cars was an unconstitutional search under the Fourth Amendment, but the justices differed on the rationale. Scalia, in a majority opinion joined by Chief Justice John Roberts and Justices Anthony Kennedy and Clarence Thomas, argued the tracking device was an unconstitutional trespass on Jones’s property. Justice Samuel Alito, in a concurrence joined by Justices Stephen Breyer, Ruth Bader Ginsburg, and Elena Kagan, rejected what he described as an “18th-century tort law” approach. Instead, he argued the tracking violated Jones’s reasonable expectation of privacy.

Sotomayor broke the tie and sided with Scalia. But her concurrence went into even greater detail about the risks that new technologies like GPS surveillance would pose to individual privacy and the Fourth Amendment’s protections.

GPS monitoring generates a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations. The Government can store such records and efficiently mine them for information years into the future. And because GPS monitoring is cheap in comparison to conventional surveillance techniques and, by design, proceeds surreptitiously, it evades the ordinary checks that constrain abusive law enforcement practices: limited police resources and community hostility.

To that end, Sotomayor wrote it may be necessary for the Court to revisit the third-party doctrine, a core component of modern interpretations of the Fourth Amendment. Under the doctrine, which emerged out of Supreme Court rulings on wiretapping in the 1970s, a person forgoes any reasonable expectation of privacy when handing over his or her personal information to third parties like corporations or banks. In other words, telephone calls between two people are generally protected from warrantless intrusion; a telephone company’s record of phone numbers a specific customer has dialed is not.

“This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks,” Sotomayor wrote in the concurrence, which no other justice joined. “People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers.”

Some may find the loss of privacy in the digital age inevitable, Sotomayor added. “[But] I for one doubt that people would accept without complaint the warrantless disclosure to the Government of a list of every Web site they had visited in the last week, or month, or year.” Her concurrence in Jones came one year before Edward Snowden, the National Security Agency contractor, revealed the existence of secret digital-surveillance programs that swept up vast amounts of personal data belonging to Americans. Lawsuits challenging those programs are working their way through the federal courts.

Sotomayor’s warnings have paralleled other major news events that revealed limits to the Fourth Amendment’s protections. As police shootings of unarmed black men reached new levels of public scrutiny last year, her warnings seemed to gain new urgency during the 2014-2015 term. In the case Heien v. North Carolina last December, the Supreme Court ruled in favor of an officer whose mistaken understanding of the law led to a man’s arrest and conviction. A North Carolina police officer pulled over Nicholas Heien and another man because their car had a broken brake light, though state law only required one working brake light. During the stop, the officer then searched the vehicle and found a small bag of cocaine.

Chief Justice Roberts, writing for an 8-1 majority, found no fault with the officer’s enforcement of a nonexistent law that preceded the search. “To be reasonable is not to be perfect,” he argued, “and so the Fourth Amendment allows for some mistakes on the part of government officials, giving them fair leeway for enforcing the law in the community’s protection.”

Sotomayor alone dissented. The Court’s precedents grant some flexibility on an officer’s perceptions of the facts when justifying a search, she argued, but had not previously extended that leeway to mistaken perceptions of the law itself. “Departing from this tradition," she warned, “means further eroding the Fourth Amendment’s protection of civil liberties in a context where that protection has already been worn down.” Slate’s Dahlia Lithwick noted that the Court’s discussions ignored “a long, sordid history of pretextual and harassing traffic stops [that] have fostered fear and anxiety in minority communities.”

The next month, the Court heard oral arguments in Rodriguez v. United States, in which Missouri police delayed a motorist after a lawful traffic stop so another officer could bring drug-sniffing dogs to search his vehicle. A Justice Department lawyer argued the Court should grant cops enough leeway to retrieve a dog from elsewhere for the search. Sotomayor disagreed.

“We can't keep bending the Fourth Amendment to the resources of law enforcement,” she told the Justice Department lawyer. “Particularly when this [search] is not incidental to the purpose of the stop. It's purely to help the police get more criminals, yes. But then the Fourth Amendment becomes a useless piece of paper.” She subsequently joined the 6-3 decision in April in favor of the defendant.

As Heien and Mullenix show, Sotomayor’s stance on the Fourth Amendment’s limits can be a lonely one. But her views seemed to influence her colleagues in one crucial case. In June 2014, the Supreme Court unanimously ruled in Riley v. California that police must obtain a warrant before searching a cell phone during an arrest. Past Supreme Court decisions carved out a Fourth Amendment exception that allows police to search a suspect’s person during an arrest for safety reasons and to prevent the destruction of evidence.

But Chief Justice Roberts, writing for the Court in Riley, noted that cell phones and similar devices are qualitatively different than other physical possessions that Americans regularly carry with them. The immense wealth of personal data that cell phones could contain, he argued, entitles them to more stringent constitutional protections than backpacks or wallets.

“The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought,” Roberts wrote. “Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is accordingly simple— get a warrant.”

Other end-of-term decisions overshadowed Riley in news coverage at the time, but the ruling’s long-term impact will be immense. Millions of Americans’ cell phones are now constitutionally shielded from warrantless intrusion during mundane arrests. And as technology plays a greater role in Americans’ everyday lives, Riley’s emphatic defense of digital privacy will likely shape the future of the Fourth Amendment. Tucked away in Roberts’ elegant reasoning was a citation of United States v. Jones—not of the majority opinion itself, but of Sotomayor’s prescient concurrence to it.

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