Heien v. North Carolina
The Supreme Court ruled that a traffic stop can still be valid even when the officer was mistaken about what the law actually required, so long as that misunderstanding was a reasonable one. The officer here stopped a car for a single broken brake light, wrongly believing state law required two working brake lights.
The decision means police no longer need to get the law exactly right to justify a stop — only reasonably right — expanding the situations in which evidence found during a stop, like the cocaine discovered here, can be used against a defendant.
“Reasonable suspicion arises from the combination of an officer's understanding of the facts and his understanding of the relevant law.”
The majority's core rationale for treating mistakes of law like mistakes of fact.
How it got here: A trial court denied suppression; the North Carolina Court of Appeals reversed; the North Carolina Supreme Court reversed that and upheld the stop, prompting the U.S. Supreme Court to grant review.
The Case in Depth
What happened
A sheriff's sergeant in North Carolina pulled over a car after noticing only one of its two brake lights worked. During the stop he grew suspicious of the two occupants and, with the owner's consent, searched the car and found cocaine in a duffel bag. The driver's passenger, who owned the car, was charged with attempted cocaine trafficking and sought to have the evidence thrown out.
The question before the Court
If a police officer pulls someone over based on an honest, reasonable misunderstanding of what a traffic law actually requires, is that stop still legal?
The Court's answer
Yes — the Court ruled that a traffic stop can rest on reasonable suspicion even when the officer's understanding of the law, not just the facts, turns out to be mistaken. Reasonable suspicion depends on both what an officer reasonably believes about the facts and what an officer reasonably believes the law requires, and a reasonable error in either respect produces the same result: conduct that reasonably appeared to break the law.
Here, the North Carolina brake-light statute was genuinely confusing, referring to "a stop lamp" in the singular while also requiring "all originally equipped rear lamps" to work, and no state court had ever interpreted it before. Because it was objectively reasonable for the officer to read the law as requiring two working brake lights, the stop was valid even though a court later decided only one light was legally required.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Drivers can now be lawfully pulled over even when the officer misunderstood an ambiguous traffic law, so evidence found during such stops can still be used in court. The ruling gives police more legal cover when statutes are unclear, while critics worry it leaves drivers with less certainty about what conduct can trigger a stop.
What changes now
This is a final merits decision, not a temporary order. The North Carolina Supreme Court's judgment upholding the stop and the cocaine-trafficking conviction stands. Because the holding applies nationally to Fourth Amendment reasonable-suspicion analysis, other courts must now consider whether an officer's legal error was objectively reasonable, not just whether officers got the facts right, when evaluating the validity of stops based on ambiguous or previously uninterpreted statutes.
What this does not decide
The Court did not decide that mistakes about the Fourth Amendment's own requirements can excuse a stop — Justice Kagan's concurrence stresses that errors about constitutional limits themselves are never excused. The Court also required that the legal error be objectively reasonable, not simply any officer's sincere but sloppy misreading of a statute.
Concurrences and dissents
Concurrence — Justice Kagan
Justice Kagan agreed with the majority but wrote to stress two limits: an officer's subjective ignorance or poor training never justifies a legal mistake, and the reasonableness test for mistakes of law is more demanding than the test used for qualified immunity. She said the test is met only when a statute poses a genuinely difficult interpretive question, which she called an 'exceedingly rare' situation, and found the North Carolina brake-light statute's conflicting provisions met that high bar.
Dissent — Justice Sotomayor
“I would hold that determining whether a search or seizure is reasonable requires evaluating an officer's understanding of the facts against the actual state of the law.”The dissent's central objection to allowing mistakes of law to justify a stop.
Justice Sotomayor argued that reasonableness review has always asked whether an officer's understanding of the facts, not the law, was reasonable, because courts — not officers — are best positioned to say what the law means. She warned that letting legal mistakes justify stops discourages courts from ever clarifying ambiguous statutes, burdens innocent citizens who cannot know what conduct might trigger a stop, and finds no real support in the Court's cited precedents. She would hold that no mistake of law, however reasonable, can justify a stop.
How the Court got there
The legal reasoning, step by step
- The Court framed the question as whether reasonable suspicion for a traffic stop can rest on an officer's reasonable mistake about what the law itself requires, not just a mistake about the facts on the ground.
- The Court explained that the Fourth Amendment only demands reasonableness, not perfection, and it has long tolerated reasonable mistakes of fact — such as an officer who reasonably believes a stranger has authority to consent to a home search when the person does not actually live there.
- The Court reasoned that reasonable suspicion is built from both an officer's understanding of the facts and an officer's understanding of the relevant law, so a reasonable error in either component produces the same practical result: conduct that reasonably, even if wrongly, appears to violate the law.
- The Court found support in two centuries of cases, including a 1979 case, Michigan v. DeFillippo, holding that officers had probable cause to arrest someone under an ordinance later declared unconstitutional, because their assumption the law was valid was reasonable at the time.
- The Court limited this tolerance by requiring that any mistake of law be objectively reasonable, judged without regard to the individual officer's subjective knowledge or training, and stricter than the more forgiving standard used for qualified immunity in civil lawsuits against officers.
- Applying that objective standard, the Court concluded the North Carolina brake-light statute's conflicting language about a singular 'stop lamp' versus 'all originally equipped rear lamps,' combined with the absence of any prior court interpretation, made the officer's reading of the law reasonable.
Doctrinal impact
Cases affected by this decision
Reaffirms Michigan v. DeFillippo (443 U.S. 31)
The Court relied on this 1979 case as supporting that a reasonable but mistaken legal assumption can still produce valid probable cause.