Why police aren't expected to know the law even as they arrest you for breaking it

Last December, the Supreme Court ruled that police officers can pull someone over without a legitimate legal justification as long as they reasonably misunderstand the law to allow the stop. Critics were quick to point out that this effectively lets cops pull people over for just about any reason — as long as they reasonably claim ignorance of the law.

Well, it looks like critics were right. The Marshall Project's Ken Armstrong explained the aftermath of the Supreme Court's decision in Heien v. North Carolina:

In the eight months since, courts in at least a dozen states have excused mistakes made by police who initiated stops based on a misunderstanding of what is legal and what is not, according to a canvass of court rulings. Police from California to Kansas to Illinois to New Hampshire proved ignorant of the law on items ranging from tail lights to turn signals to tinted windows to fog lines to U-turns to red lights — only to be rewarded for it, as judges, in the typical scenario, refused to throw out evidence (drugs, most often) seized as a result of the ill-founded stops.

Armstrong details some of the most striking cases, including several examples of cops pulling people over for having air fresheners in their rearview mirror. Even though the initial reasons for the stops weren't legitimate, judges said cops reasonably mistook the law, and could therefore use the evidence gathered at the stops for trial.

One of the cases detailed by Armstrong shows courts reversing their opinion in a matter of months due to the Supreme Court ruling. In The People v. Felipe Campuzano, an appellate court in San Diego County said on November 2014 that police mistook the law, so the evidence they had gathered at a stop for a DUI charge was invalid. Then the Supreme Court handed down its December decision, and the San Diego County court flipped — allowing the cops to use the evidence in trial after all.

It's one thing to not punish the cops for wasting people's time during unlawful traffic stops. But these cases go even further — showing a clear expansion of police powers, in which cops aren't expected to know the law even as they arrest people for breaking it.

Watch: Why filming the police is so important

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