SCOTUSblog explains Opinion analysis: Reasonable mistakes of law by police do not violate the Fourth Amendment. "The exercise of police discretion to stop people on the street is front and center in today’s headlines. In this case, a North Carolina policeman stopped Heien’s car because it had a brake light that did not work. During the stop, Heien consented to a search of the car, which yielded cocaine in a duffle bag and Heien’s ultimate conviction for attempted drug trafficking. On appeal, the North Carolina appellate courts surprisingly ruled that the outdated state vehicle code required only one working brake light (‘a’ stop lamp, in the words of the statute); therefore, there had been no violation of law that would permit the stop. The officer made no error about the facts; but he had been mistaken about the meaning of the law. However, the North Carolina Supreme Court ruled, the officer’s mistake about this law was ‘reasonable,’ and for that reason the Fourth Amendment right to be secure from ‘unreasonable … seizures’ was not violated. This morning’s [8-1] opinion in Heien v. North Carolina affirms that holding."