Peugh v. Porter & Another was a United States Supreme Court case that addressed the issue of whether a defendant could be convicted of a crime based on evidence that was obtained after the statute of limitations had expired. The case involved a man named Peugh, who was accused of embezzling money from his employer. The statute of limitations for the crime had expired before the evidence was obtained, but the prosecution argued that the evidence should still be admissible in court. The Supreme Court ultimately ruled in favor of Peugh, finding that the evidence should not be admissible in court. The Court reasoned that allowing the evidence to be used would violate the defendant's right to due process, as the statute of limitations was intended to protect defendants from being convicted of crimes based on stale evidence. The Court also noted that the prosecution had failed to show that the evidence was necessary to prove the defendant's guilt. As a result, the Court held that the evidence should not be used in court, and the defendant's conviction was overturned.

In the case of Peugh v. Porter & Another, the Supreme Court was asked to decide whether a defendant had been denied due process when he was sentenced under an amended version of the federal sentencing guidelines that increased his sentence from 33 months to 70 months. The majority opinion held that there had not been a violation of due process because it is reasonable for Congress to amend criminal statutes and sentencing guidelines in order to increase punishments for certain offenses. Justice Breyer dissented, arguing that such retroactive application violates principles of fair notice and fundamental justice by punishing individuals more harshly than they could have reasonably anticipated at the time they committed their crimes. He argued further that this type of punishment should only be applied prospectively so as not to punish people unfairly or unconstitutionally based on laws passed after their actions were taken.