Editorial: Police need to know the laws they enforce

“Ignorance of the law is no excuse” — except when you’re a police officer. That’s essentially the argument the state of North Carolina made to the U.S. Supreme Court last week when it defended the drug conviction of a man whose car was stopped by police based on a misunderstanding of a state traffic law.

Great constitutional cases often involve small-time offenses and routine police work, and this is no exception. When an officer in the Surry County Sheriff’s Department saw a Ford Escort with a broken right brake light, he pulled the car over and told the occupants he was citing them “for a nonfunctioning brake light.” Apparently suspicious, the officer asked the owner of the car, Nicholas Heien, if he could search it.

The search turned up a plastic sandwich bag containing cocaine, and Heien was arrested. But then an interesting fact emerged: North Carolina law says that no person may operate a motor vehicle “unless it shall be equipped with a stop lamp on the rear of the vehicle.” Heien’s Escort had “a” working brake light — the left one. The issue for the North Carolina courts, and now for the Supreme Court, is whether the stop was reasonable under the 4th Amendment. If the Supreme Court rules that it wasn’t, Heien can return to the state courts and argue that the evidence should be excluded.

In previous decisions, the court has held that evidence from a search can be admitted at trial if the police made a “good faith” mistake of fact — such as relying on a warrant that contained the wrong address. But mistakes of law are another matter. Heien’s lawyers concede in their brief that “officers need flexibility to make quick, ad hoc factual assessments in the field — and they are expert in doing so. The law, by contrast, lends itself to careful … analysis.” A police officer can’t read up in advance on every factual contingency or be expected to know that a search warrant is defective. But he can study the law at his leisure before he has to enforce it. And if police aren’t penalized for making stops based on ignorance of the law, they won’t have any incentive to educate themselves.

Because traffic codes are filled with minor and sometimes arcane requirements, it’s already too easy for police to stop a car ostensibly because of a minor infraction but actually because they have a hunch that the vehicle contains drugs or other evidence of a serious crime. It would undermine the protections of the 4th Amendment even more if police could stop and possibly search a car because of a violation of a law that existed only in the officer’s mind. The Supreme Court must hold law enforcement to a higher standard.

Follow the Opinion section on Twitter @latimesopinion