Laws change all the time. But imagine if something you did two years ago suddenly became illegal today. Would it be fair to throw you in jail now? Our Constitution says no.

The United States Constitution prohibits “ex post facto” laws. This means the government cannot alter criminal laws “after the fact”. This blog provides an overview of the ex post facto clause and how it may apply in criminal cases.

The ex post facto clause serves several important purposes.

First, it allows us to rely on the laws as they are written. Consider someone deciding to start a liquor import business in the early 1900s. That person should be able to confidently start that business without fear that liquor may become illegal a few years down the road.

Second, prohibiting ex post facto laws promotes fundamental fairness. Laws are prone to change with the tides of politics. Marijuana, alcohol, gambling, abortion, and smoking are all topics which are viewed very differently today than they were in the past.

Other laws become necessary as the world changes. Things like sharing nude photos, artificially generated pornography, new chemically engineered narcotics, or flying a drone in restricted spaces have all required the creation of new laws. While we may all agree these new things should be punished, our system requires laws to be created through the legislative process.

Third, preventing ex post facto laws restrains the government by preventing vindictive legislation. As put by Alexander Hamilton, the retroactive “creation of crimes” has been “in all ages, the favorite and most formidable instrument of tyranny.”

What types of laws are prohibited.

The ex post facto clause applies only to criminal and penal laws, not civil regulations. Imprisonment and fines are traditionally considered criminal penalties. Additionally, retroactively removing a defense that existed at the time of the crime, like a statute of limitations, has been found to violate the ex post facto clause.

On the other hand, significant restrictions like no contact orders and predatory offender registration are considered civil regulations. These laws can be changed after the fact and impose new burdens on old criminal conduct, even years after the crime.

Deciding if a law is criminal or civil is very case specific. To decide, courts will consider many different factors, including:

• If the law affirmatively disables or restrains someone.
• If the type of law has historically been considered criminal.
• If the law requires some type of guilty intent or purpose.
• If the law is aimed at retribution and deterrence.
• If the behavior regulated is already a crime.
• If there is another purpose for the law other than criminal punishment.
• If the punishment appears excessive compared to any alternative purpose.

How your lawyer can help.

Hiring a lawyer can help you determine if the ex post facto clause will apply in your case. Your lawyer will be up to speed with recent and historical changes in the law that might affect your case. They will know how to research what specific date a new law came into effect. Additionally, your lawyer will know how to find case law to help persuade the judge that the ex post facto clause should apply to your case. Lastly, they will be able to write and file the necessary motions to argue the issue in court.

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If you or someone you know has been accused of a crime in Minnesota, don’t wait to get the legal help you need. Contact McKinney Defense today by calling (612) 300-1208 or filling out our online form to schedule a FREE consultation. Let me fight for your rights and help you take the first step toward fair representation.

Copyright © 2025 McKinney Defense PLLC. All rights reserved. This blog post (“post”) is provided for general informational purposes only and may not reflect the current law in Minnesota or your jurisdiction. No information in this post should be construed as legal advice from the individual author or the law firm, nor is it intended to be a substitute for legal counsel on any subject matter. No reader of this post should act or refrain from acting based on any information included in or accessible through this post without seeking the appropriate legal or other professional advice on the particular facts and circumstances at issue from a lawyer licensed in the recipient’s state, country, or other appropriate licensing jurisdiction.