It used to be that when police violated a suspect’s Fourth Amendment rights through an unconstitutional search, evidence derived from the search would be thrown out.

Increasingly, that’s not the case.

Courts are carving out ever-larger safe harbors for police errors and misconduct, thereby eroding the boundaries of the Fourth Amendment prohibition on unreasonable search and seizure. Earlier this month, the 3^rd Circuit Court of Appeals became the latest to give the government a free pass for Fourth Amendment violations—in this case, allowing use of evidence derived from a GPS tracking device that police attached to a suspect’s van without a warrant.

Under the “exclusionary rule,” when police engage in an illegal search, prosecutors can’t use the results. This penalty incentivizes police to abide by the Constitution and provides relief to victims of government misconduct. Indeed, as the Supreme Court explained a century ago, without the exclusionary rule the Fourth Amendment would be “of no value” and “might as well be stricken from the Constitution.”

But in a series of decisions starting in 1984, the Supreme Court has retreated from this vital protection of our rights. The justices first held that if police were relying in good faith on a judicially issued warrant authorizing a particular search, the resulting evidence couldn’t be suppressed even if the search was later held to be unconstitutional. The court has since expanded this good-faith exception to cover police reliance on other forms of explicit authorization, including statutes later held to be unconstitutional and binding court rulings that are later reversed.

The theory behind these Supreme Court decisions is that the exclusionary rule’s purpose is not to help people whose rights have been violated, but to deter police from committing violations. When police are following guidance from an authoritative outside source, the theory goes, they are doing what they are supposed to do. Suppressing evidence won’t deter future violations because police couldn’t have been any more careful. Unfortunately, this view of the Fourth Amendment leaves defendants without relief for unconstitutional police conduct. (A similar doctrine, qualified immunity, often prevents people from securing compensation for Fourth Amendment violations in civil suits against offending police officers.)

Perhaps even worse, the good-faith exception to the exclusionary rule stunts the development of Fourth Amendment law. It discourages defendants from challenging illegal searches by denying them the possibility of redress. And courts frequently apply it without also addressing whether police conduct actually violated the Fourth Amendment in the first place. Whatever you think about the good-faith exception, courts are using it as an excuse to avoid scrutinizing questionable police searches.

For instance, last year, a three-judge panel of the 3^rd Circuit held in United States v. Katzin that FBI agents violated the Fourth Amendment when they placed a GPS tracker on a Pennsylvania man’s vehicle without a warrant. The court ordered the GPS-derived evidence suppressed. The panel’s decision was important, because it was the first appellate opinion to hold that a warrant is required for GPS tracking since the Supreme Court’s 2012 decision in United States v. Jones. In that case, the court found that attaching a GPS device to a car and tracking the car’s movements is a Fourth Amendment “search,” but did not decide whether it is the kind of search that requires a warrant, leaving that important question to lower courts to figure out. (I worked on the amicus briefs filed by the American Civil Liberties Union for Katzin and other cases involving the good-faith exception.)

Borrowing language from Justice Sonia Sotomayor’s concurring opinion in Jones, the 3^rd Circuit panel explained that a warrant is required because GPS trackers can record “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.”

After losing in Katzin, the government sought rehearing by the full 3^rd Circuit. It argued that the good-faith exception should apply even though there was no binding judicial decision permitting warrantless GPS tracking at the time of the search. On Oct. 1, the full appeals court took the government’s side. While radically expanding the scope of the good-faith exception, the court also vacated the portion of the original panel opinion that required a warrant for future GPS tracking.

Every other court of appeals to have considered warrantless GPS tracking since Jones has likewise avoided opining on whether a warrant is required, meaning the good-faith exception has become a shield against meaningful judicial review. This shirking of judicial responsibility leaves police without guidance on what the Constitution requires and people vulnerable to encroachments on their privacy. If courts never say what the Fourth Amendment requires, police will never be forced to comply with it.

The 3^rd Circuit’s decision only feeds the good-faith exception’s malignant growth. The court held that it was reasonable for law enforcement to not seek a warrant based on a combination of outdated Supreme Court opinions about obsolete “beeper” tracking technology, the nonbinding decisions of other circuit courts, and the advice of a prosecutor, who has an incentive to approve overly aggressive police investigative practices.

The five dissenting judges excoriated this approach for “expand[ing] the good faith exception to the point of eviscerating the exclusionary rule altogether by failing to provide any cognizable limiting principle. Now, law enforcement shall be further emboldened knowing that the good faith exception will extricate officers from nearly any evidentiary conundrum.”

If police can rely on any mushy combination of nonbinding factors to justify an unconstitutional search, the Fourth Amendment becomes immeasurably weaker. And if courts decline to even say what the Fourth Amendment means, we are left at the mercy of investigators’ self-interested decisions, without the scrutiny of an independent judge.

Unfortunately, decisions like the 3^rd Circuit’s recent one create a climate of government impunity and weaken our system of protections against overzealous searches. In the coming months, several more appellate courts will have an opportunity to consider whether GPS evidence acquired without a warrant can be introduced at trial. And defendants in cases where courts have expansively interpreted the good-faith exception have petitioned for Supreme Court review.

In one case awaiting oral argument in the 8^th Circuit, police used a battery-powered GPS tracker on a Missouri man’s car for nearly two months without a warrant, cataloging his every move as he traveled around the greater St. Louis area. In another case, police used a GPS device to track a man as he traveled in Maryland and West Virginia for nearly a month, also without a warrant. After a three-judge panel of the 4^th Circuit invoked the good-faith exception, the defendant petitioned the full 4^th Circuit for rehearing (the court has yet to act). This kind of long-term location tracking threatens the core protections of the Fourth Amendment by exposing voluminous details of people’s private lives to police scrutiny. 

In these and other cases, there is still a chance for courts to get it right.

As our judicial system struggles to apply the Fourth Amendment’s protections to new kinds of searches in the digital age, instituting proper safeguards against unwarranted police surveillance will become ever more important. Courts that keep contriving new ways to accommodate the police should remember that the Fourth Amendment’s protections—what Justice Thurgood Marshall described as “an essential bulwark against arbitrary and unreasonable governmental intrusion”—can only erode so far. If we’re not careful, some day we might realize those vital protections have withered away completely.