What is ex post facto law?

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The 1987 Philippine Constitution explicitly prohibits the enactment of any ex post facto law. In general, the doctrine against ex post facto laws prohibits the retroactive application of penal or criminal laws if such application is prejudicial or unfavorable to the accused. This aligns with the legal maxim nullum crimen, nulla poena sine lege—there is no crime when there is no law punishing it.

Characteristics

An ex post facto law has three essential characteristics:

1. It refers to criminal or penal matters.
2. It is retroactive in application.
3. It works to the prejudice of the accused.

Six Kinds of Ex Post Facto Laws

A law is considered an ex post facto law if it falls under any of these six categories:

1. It criminalizes an act that was done before the passing of the law and was innocent when committed.
2. It aggravates a crime, making it greater than it was when committed.
3. It changes the punishment, inflicting a greater or more severe penalty than what was provided by law when the crime was committed.
4. It alters the legal rules of evidence, allowing the use of less or different testimony to convict the offender than what was required at the time the offense was committed.
5. It assumes to regulate civil rights and remedies only, but in effect imposes a penalty or deprives a right for an act that was lawful when done.
6. It deprives a person accused of a crime of a lawful protection to which they have become entitled, such as the protection of a former conviction, an acquittal, or a proclamation of amnesty.

Scope and Exceptions

• Civil vs. Penal: The prohibition generally applies only to criminal or penal matters, not to civil proceedings or laws regulating civil rights.
• Exceptions for Non-Penal Acts: Even if an issuance is not strictly a penal law (like an executive proclamation), it can violate the ex post facto prohibition if it retroactively strips a person of a lawful protection against criminal prosecution, such as revoking an already vested amnesty.
• Extradition: The constitutional prohibition against ex post facto laws does not apply to extradition treaties.
• Preventive Suspensions: A law imposing a suspension on public officers pending investigation is not considered an ex post facto law because the suspension is merely a preventive measure, not a punitive one.