"It has been held from the earliest days, in both the Federal and state courts, that a mistake of law, pure and simple, without the addition of any circumstances of fraud or misrepresentation, constitutes no basis for relief at law or in equity, and forms no excuse in favor of the party asserting that he made such mistake."
That is a quote from the Supreme Court's decision in Utermehle v. Norment, 197 U.S. 40, 56 (1905) (we cited this case, instead of another, because the name is pretty cool).
We learned last December, however, that this time-tested rule has an exception for police officers. We blogged about that case (Heien v. North Carolina) here. That's right. If our clients act upon a mistake in the law, too bad, but if a police officer does, well, so what. With one exception: unreasonable mistakes of law, even committed by police officers, would not form an excuse for improper conduct (in this context, an unconstitutional search or seizure).
Now, full disclosure, we doubted the day would come that a court actually found an officer's mistake of law unreasonable.
We were wrong.
It happened. Already.
In United States v. Alvarado-Zarza, the Fifth Circuit reversed the denial of a suppression motion because a traffic stop based on a failure to signal 100 feet in advance of a turn was premised on an unreasonable mistake of law. The problem (for the officer anyway) was that the vehicle did not actually turn; it simply changed lanes. Under Texas law, the signal-100-feet-in-advance requirement is for turns, not lane changes. Hence, a mistake of law.
In determining whether this mistake was unreasonable, the Fifth Circuit distilled a two-pronged analysis from Heien: (1) whether the statute at issue was ambiguous; and (2) whether the state's appellate courts had interpreted the statute. It held that the statute was not ambiguous (it clearly applied only to turns, as confirmed by other statutes and even the Texas Driver's Handbook). Moreover, a Texas state appellate court recently issued a decision discussing the differences between turns and lane changes (calling the distinction "plain and unambiguous"). So, the officer made an unreasonable mistake of law. Suppression was warranted.
There was a secondary issue because the defendant ultimately turned (he went from a through-lane to a turn-lane without signaling, then signaled prior to turning from the turn lane). The question was whether the defendant actually signaled more than 100 feet prior to turning. The defendant provided testimony from an expert who measured the distance at 300 feet (the incident was caught on a dash cam, which allowed the expert to identify the relevant points (when the defendant signaled and when the defendant actually turned)). The government argued that the officer's mistake of fact (I thought it was less than 100 feet) was reasonable. The Court disagreed, noting that the officer testified that he acted quickly without paying much attention to the distance (and don't forget, the officer did not know the law either).
When Heien dropped, it had the feel of an historically bad decision (for fans of the Fourth Amendment). It still is, but the Fifth Circuit has lessened the sting a bit.