State v Helen, arose out of North Carolina. The facts, on the surface, were about as favorable as it gets for the prosecutor.
The accused had a tail light out. [If I had a dime for every defendant I represented who was pulled over for a tail light...] The officer stopped the motorist; the stop led to a search of his vehicle and, eventually, a drug conviction.
Here is the problem that arose on appeal: in North Carolina, there is a little known wrinkle in their motor vehicle code which provides that, so long as a motorist's other tail light is functioning, having one light out is not a violation.
This case went all the way to the North Carolina Supreme Court. Now, if I was sitting on that High Court, my vote would be to reverse the conviction. If the officer lacked probable cause to conduct a traffic stop, then basic Fourth Amendment constitutional law provides that the evidence seized in an illegal stop and search is excluded as the proverbial "fruit of the poisonous tree".
A constitutional "no-brainer", right? Guess again. The divided High Court essentially created a new traffic law by holding that, so long as the officer held a reasonable belief that a law had been broken, the search was legal.
But citizens, take note that this "reasonably-held-belief" standard does not work both ways. If you, the motorist, reasonably believe that you are obeying the traffic laws, [say you are texting in a municipality where you believe no distraction ordinance has been adopted], but in fact, you are violating a provision of the traffic code, then your ignorance of this law is no defense and you can get a ticket.
The "take away" from this case from North Carolina is that ignorance of the law is ok if you are a peace officer, but not if you are an ordinary citizen.