Criminal Law

Ex post facto laws are laws that work to retroactively make conduct previously legal illegal, retroactively increase a punishment, retroactively change the rules of evidence in a criminal case, or retroactively alter the definition of a crime. Ex post facto laws are prohibited by the Constitution. The framers believed it was imperative to provide citizens with some idea of what behavior could be punished, and that it was important to prevent tyranny by those in power.

Criminal statutes also need to be understandable to persons of ordinary intelligence. If a reasonable person cannot determine what a law is trying to command or prohibit, that law will be struck down as being void for vagueness. The doctrine of vagueness comes from the Due Process Clauses of the Fifth and Fourteenth Amendments to the Constitution. Laws prohibiting vagrancy have sometimes come under attack as being void because of language that fails to provide an adequate warning as to the type of conduct that might offend the law.

The Eighth Amendment's prohibition against cruel and unusual punishment prohibits punishment which is cruelly disproportionate to the crime. The Supreme Court has ruled that a sentence of 15 years of hard labor was a constitutionally prohibited punishment for a pubic official who falsified a minor document. Likewise, a death sentence for a convicted rapist has also been ruled to constitute cruel and unusual punishment.