If you’re a follower of criminal defense cases like we are, then you know how often disputes arise in the courtroom about the interpretation of the Fourth Amendment. As many of you know, the Fourth Amendment “protects people from unreasonable searches and seizures by the government.” A violation of this right precludes evidence from being used at a criminal trial.

But as many court cases have pointed out over the years, the difference between a violation of a person’s constitutional rights and a lawful search depends heavily on whether the search was considered reasonable or not. This was the crux of the U.S. Supreme Court case of Heien v. North Carolina.

In the case, an officer arrested an individual after finding drugs during a traffic stop. The defendant argued that the evidence against them should not be admissible in court because the officer misunderstood the law that led to the traffic stop. The question before the court then was: if the law had been correctly interpreted, would the officer have had the reasonable suspicion necessary to uphold the search and seizure of drug evidence?

In an 8-1 decision made this month, the U.S. Supreme Court answered this question by upholding a lower court decision that considered the traffic stop valid despite the mistake of the law. As the court explained, the term reasonable does not necessarily mean perfect, meaning the Fourth Amendment does allow for some mistakes.

It’s important to note though that this does not mean law enforcement has the right to blatantly violate the law and a person’s constitutional rights. Reasonable suspicion is still necessary — as well as the consent of the accused or a warrant — in order to conduct a search. As you can imagine though, this may be difficult to argue without a lawyer, especially because the law determines what is reasonable and what is not.