Last Updated on July 2, 2025
You’ve no doubt heard the expression that “ignorance of the law is no excuse,” and while that’s true in most cases, it’s not the full story. For one thing, there are a handful of laws that are only crimes if the defendant knew they were breaking the law -for example, it is illegal to bring more than $10,000 in cash into the country without declaring it to U.S. Customs. But this is one of the few laws where the prosecution must be able to prove that you not only committed the act, but also knew it was illegal. In these rare situations, ignorance of the law is actually something your defense attorneys can use to fight the charges.
The Legal Principle of Mens Rea
Situations where ignorance of the law is a full defense are notably rare. More often though, the concept of “mens rea” comes into play. This phrase is Latin for “guilty mind” and basically means you need to have a wrongful intent to be guilty of a crime. Knowledge and intent are issues in most cases. In fact, this is one of the core concepts behind the insanity defense, as the Supreme Court has upheld the belief that if a person is unable to comprehend whether something is right or wrong, they cannot be accountable for certain actions.
When is Ignorance a Criminal Defense?
While insanity pleas only apply to certain situations, the idea of “mens rea” applies to many other situations. For example, if you were transporting drugs in your vehicle, but did not know they were there because someone else planted them without your knowledge, if your attorneys can show that you had no knowledge that you were transporting drugs, you cannot be convicted. In other words, while ignorance of the law might not always be a defense, not knowing that you were committing a crime might be.
A Lack of Knowledge as a Partial Defense
In some cases, the defense may not be able to protect you from conviction altogether, but it could mean you will face much less severe charges. For example, if you killed someone during a fight, you can only be charged with murder if you had an intent to kill -for example, if you started to choke the victim. If a punch happened to land in the wrong place, causing the victim to die without any intent on your part, your defense lawyer may be able to have the charges dropped to manslaughter.
That being said, although it was previously commonly thought one unintended fatal punch cannot be murder, the California Supreme Court held in the La Jolla Bird Rock Bandit case, under certain circumstances, one lethal punch may be murder. If you only hit the victim because you thought they were going to attack you, then your criminal attorneys will have an additional defense against the charges because they can argue you acted in self-defense.
If you have any questions about how ignorance of the law or “mens rea” may affect your case, please contact skilled criminal defense attorney Peter M. Liss at (760) 643-4050 to schedule a free initial consultation.
