In Heien v. North Carolina, the Supreme Court will decide whether reasonable suspicion to stop a vehicle can be based on a police officer’s reasonable mistake of law. In this case, the sergeant observed the defendant driving with only one brake light and, believing that this violated North Carolina traffic laws, the sergeant pulled the car over. The familiar pattern of a consent search and discovery of drugs followed in due course. At trial the defendant argued that he was not in fact in violation of the traffic laws and therefore the stop was unconstitutional. The lower court disagreed, holding that it was in fact illegal for the defendant to drive with only one brake light, but the intermediate appellate court reversed, engaging in a lengthy discussion of the North Carolina Traffic Code an ultimately concluding that a driver may legally operate a car with only one brake light. Thus, the appellate court concluded that the stop was unconstitutional and therefore the drugs should be suppressed.
The prosecution appealed to the North Carolina Supreme Court, but interestingly enough, it did not appeal the question of whether it is legal to drive with one brake light. Instead, it argued that the stop was constitutional because the sergeant had a reasonable and good faith belief that the defendant was breaking the law. In a 4-3 decision, the court agreed with the government’s position and upheld the search:
We are not persuaded that, because Sergeant Darisse was mistaken about the requirements of our motor vehicle laws, the traffic stop was necessarily unconstitutional. After all, reasonable suspicion is a “commonsense, nontechnical conception  . . . on which reasonable and prudent men, not legal technicians, act,” and the Court of Appeals analyzed our General Statutes at length before reaching itsconclusion that the officer’s interpretation of the relevant motor vehicle laws was erroneous.
Many of those who oppose the decision of the North Carolina Supreme Court (including the three justices who dissented) argue that allowing a reasonable mistake of law to form the basis of reasonable suspicion would represent a significant step in the perceived erosion of our Fourth Amendment rights. For example, the dissent argued that the majority’s decision would apply:
when the officer acts based on the misreading of a less innocuous statute, or an incorrect memo or training program from the police department, or his or her previous law enforcement experience in a different state, or his or her belief in a nonexistent law.
But this is surely not the case. A police officer’s “belief in a nonexistent law” could not possibly be considered reasonable. And a mere “misreading” of a law is not reasonable—Sergeant Darisse’s mistake was only deemed reasonable because a trial court later agreed with it and the appellate court needed pages of sophisticated statutory analysis to determine that both the Sergeant and the trial court were wrong. And if the police officer is basing his or her belief on “an incorrect memo or training program from the police department,” this does not make the mistake reasonable; it simply means that the unreasonable mistake was made by someone else in the police department. (In Herring v. United States, the Supreme Court held that the exclusionary rule should not be applied in such a case because the officer acted in good faith, but that is a question of remedies, not rights. For a good analysis of this “right/remedy” distinction in the Heien case, see this blog post by Professor Rory Little).
In reality, if the Court finds that a reasonable mistake of law can be the basis of an officer’s reasonable suspicion (which it probably will), the impact of this decision will be quite limited. When is a court going to deem that a police officer’s mistake of law is reasonable? Almost never. Although the North Carolina Supreme Court rejected the defendant’s position that a police officer’s mistake of law is always unreasonable, it implied that a police officer’s mistake of law is almost always unreasonable. Heien was a very unusual case, involving an ambiguous law and a rather unexpected interpretation of the law by a appellate court. Most of the mistakes of law made by police officers (which are probably relatively rare in the first place) would not meet the reasonableness standard.
As many commentators have noted, reasonableness is becoming more and more significant in the Court’s Fourth Amendment analyses. In the past two years alone, the Supreme Court has applied a reasonableness test to preclude detention of suspects not present at the site where a search warrant is executed; to prohibit a per se finding of exigency to take blood samples in drunk driving cases; to allow strip searches and for those arrested for minor crimes; and to allow DNA tests for those arrested of felonies. In each of these cases, the Court avoided applying a bright-line test and instead balanced the competing interests of law enforcement and the privacy rights of suspects. From the questions at oral argument, it appears the Justices will follow the same course in this case as well.