Ex Post Facto Clause in California

Under the both the federal and California Constitutions, there are prohibitions on ex post facto laws. As a result, the Legislature cannot pass an ex post facto law, which means they cannot retroactively make an action a crime that was legal when done, aggravate a crime, or increase the punishment attached to a crime after its commission.

Note that beneficial changes are permissible under the Constitution. In other words, while the government cannot retroactively harden a criminal penalty, the Legislature can retroactively soften or mitigate penalties.

The ex post facto clause in California prohibits the state from passing retroactive criminal laws that disadvantage a defendant, mirrored by the same strict ban in Article I, Section 9 of the California Constitution and Article I of the U.S. Constitution. What does this clause prohibit?

A law violates the ex post facto prohibition if it does any of the following:

• Criminalized past conduct;

• Increasing criminal punishment (e.g., imposing a heavier penalty or longer prison sentence);

• Withhold a legal defense (e.g., taking away a defense that was available to the defendant when the act occurred);

• Ease the burden of conviction (e.g., altering rules of evidence or procedure to make a conviction easier to obtain than at the time of offense)

An example in California occurred in 1993, when the California Legislature enacted Penal Code § 803(g), which allowed old child molestation charges to be prosecuted even after the original statute of limitations had already expired. In Stogner v. California (2003), the U.S. Supreme Court struck down the law, ruling that reviving a time-barred prosecution violates the ex post facto clause because it exposes a person to criminal liability where none legally existed anymore.

There are some law changes that do not violate the ex post facto clause. For example, laws that change administrative or procedural aspects (e.g., how parole hearings are scheduled or conducted) are generally valid as long as they do not increase the actual sentence or alter substantive opportunities for release.

In addition, the ban applies strictly to criminal and penal laws, not civil regulations or administrative schemes (such as sex offender registration requirements under Megan’s Law, which courts have generally classified as non-punitive civil rules).

Finally, California’s Three Strikes sentencing enhancements have been upheld against ex post facto challenges because the enhanced penalty applies to the new current crime committed after the law was passed, using prior convictions as a sentencing factor rather than punishing the past crime twice.