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Mistake of Fact and Mistake of Law as Defenses to a Crime

Mistake of Fact and Mistake of Law as Defenses to a Crime

Mistake of Fact

Mistake of fact is a legal criminal defense under La RS 14:16. It provides the defendant a defense if he can prove that he honestly made a mistake regarding his interpretation of a fact that was necessary to support an element of the offense.

Unless there is a provision to the contrary in the definition of a crime, reasonable ignorance of fact or mistake of fact which precludes the presence of any mental element required in that crime is a defense to any prosecution for that crime.

In a trial, a defendant must be found NOT guilty if the jury finds:

  1. That the defendant was ignorant or made a mistake regarding a fact;
  2. That his ignorance or mistake was reasonable; and
  3. That his ignorance or mistake precluded the existence of the required mental intent.


Dan owns and operates a small shop where he works on lawnmowers, tools, cars, and other machines. He is known as the guy that can fix anything. He often sells parts and other items that come through his shop. Let’s assume John purchases a used four-wheeler from Dan for $1000. Although it runs, it is several years old with cosmetic wear and damage. Dan actually stole the four-wheeler days prior from a nearby hunting camp. However, Dan does not reveal this information to John. In fact, John asked him if it was “hot” and Dan replied, that it was not and that he owned it legally. So, John takes possession of the four-wheeler. Later that week, he is out running the woods and is stopped by an officer who is aware that four-wheeler was reported stolen by the true owner. John is arrested for Illegal Possession of Stolen Things.

Illegal possession of stolen things is the intentional possessing, procuring, receiving, or concealing of anything of value which has been the subject of any robbery or theft, under circumstances which indicate that the offender knew or had good reason to believe that the thing was the subject of one of these offenses.

Let’s apply the criminal defense of Mistake of Fact. John did intentionally possess the four-wheeler. But, he did NOT know or have reason to know that it was stolen. The best facts for John’s criminal defense attorney to prove at trial are that he paid a good amount for the used vehicle and that he inquired about its legality. It is up to the jury to determine if they believe John was reasonable and that he did not believe the four-wheeler was stolen.


However, if a crime definition expressly precludes mistake of fact or ignorance of fact as a defense, then that definition overrides mistake of fact as a defense. The most common example under Louisiana criminal law is the criminal charge of carnal knowledge of a juvenile under La RS 14:80 and 14:81. The charges expressly state that, “Lack of knowledge of the juvenile’s age shall not be a defense.”


Mistake of Law

Ignorance of the criminal laws is not a defense to any criminal prosecution. However, pursuant to LSA-R.S. 14:17, mistake of law which results in the lack of an intention that consequences which are criminal shall follow, is a defense to a criminal prosecution under the following circumstances:

  1. Where the offender reasonably relied on the act of the legislature in repealing an existing criminal provision, or in otherwise purporting to make the offender’s conduct lawful; or
  2. Where the offender reasonably relied on a final judgment of a competent court of last resort that a provision making the conduct in question criminal was unconstitutional.

It is a rare situation when a defendant does not have criminal intent because he relied on a current criminal law or high-court judgment. However, it can happen.

Example of Mistake of Law Defense

I have represented a client in this situation and we used Mistake of Law as a successful defense. This example is based on a real case, not just a hypothetical. Client was charged with Failure to Register as a Sex Offender. This is a felony charge in Louisiana. His initial conviction was for crimes against nature by solicitation under La RS 14:89.2, which initially required him to register. At some point he stopped registering as a sex offender due to a belief that the law no longer required him to register. Since the law change, there is only one provision of the statute that requires registration. That includes if the crimes against nature involved a minor. His conviction did not. This was a change to the statute.  We were able to show that he did not register because he was relying on the law. We got the case dismissed.


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