The US Supreme Court [official website] ruled [opinion, PDF] 8-1 Monday in Heien v. North Carolina [SCOTUSblog backgrounder] that a police officer’s mistake of law can provide the individualized suspicion that the Fourth Amendment [text] requires to justify a traffic stop. The case involves the arrest of an automobile passenger for cocaine possession after the driver of the automobile was pulled over for having a broken taillight. The defendant argued that, since North Carolina law [text] only requires vehicles to be equipped “with a stop lamp on the rear of the vehicle,” and the vehicle in question had one working taillight, the officer was not entitled to make the traffic stop, hence making his arrest unjustifiable. In an opinion by Chief Justice John Roberts, the court held that the officer’s mistake nonetheless gave rise to the reasonable suspicion necessary to justify the seizure under the Fourth Amendment:

But what if the police officer’s reasonable mistake is not one of fact but of law? In this case, an officer stopped a vehicle because one of its two brake lights was out, but a court later determined that a single working brake light was all the law required. The question presented is whether such a mistake of law can nonetheless give rise to the reasonable suspicion necessary to uphold the seizure under the Fourth Amendment. We hold that it can. Because the officer’s mistake about the brake-light law was reasonable, the stop in this case was lawful under the Fourth Amendment.

Justice Elena Kagan filed a concurring opinion, joined by Justice Ruth Bader Ginsburg. Justice Sonia Sotomayor filed a dissenting opinion.

The court heard arguments in the case in October after granting certiorari [JURIST reports] in April. The trial court in North Carolina v. Heien [text, PDF] denied the defendant’s motion to suppress the cocaine, but the North Carolina Court of Appeals [official website] disagreed [opinion, PDF] that all vehicular brake lights must be in working order. In November 2013 Heien petitioned [text, PDF] the Supreme Court for certiorari in this case.