In the case of Bernardo Sampeyreac and Joseph Stewart v. The United States, appellants argued that they had been wrongfully convicted for piracy under a law which was not in effect at the time of their alleged crime. Appellants claimed that Congress had passed an act repealing all prior acts concerning piracy, including one from 1790 which provided for capital punishment upon conviction. However, when they were tried before a jury in 1831, the judge instructed them to be found guilty if they committed any act defined as piratical by either statute or common law. The Supreme Court held that this instruction was erroneous because it allowed jurors to convict on evidence outside of what Congress intended with its repealer act; thus violating appellants' rights under due process clause of Fifth Amendment. Ultimately, the court reversed appellant's convictions and remanded back to lower courts for further proceedings consistent with their opinion.

In the case of Bernardo Sampeyreac and Joseph Stewart v. The United States, the appellants argued that they had been unlawfully convicted under a law which was passed after their alleged offense occurred. This argument was based on the Ex Post Facto Clause of Article I, Section 9 of the Constitution which states that no ex post facto laws shall be passed by Congress. The Supreme Court disagreed with this argument and held that since there were no criminal penalties imposed in this particular law, it did not violate the Ex Post Facto Clause as it only provided for civil remedies to those who violated its provisions. Furthermore, even if criminal penalties had been imposed in this particular statute, they would have still applied to offenses committed prior to its passage due to a long-standing principle known as "the common law rule". Therefore, because neither party could prove otherwise at trial or on appeal before the Supreme Court, Sampeyreac and Stewart's conviction stood despite their claims regarding an unconstitutional application of an ex post facto law.