United States v. Smith was a United States Supreme Court case that dealt with the issue of whether a defendant could be convicted of a crime if the indictment failed to allege the essential elements of the offense. The defendant, Smith, was indicted for the crime of receiving stolen goods, but the indictment failed to allege that the goods were stolen. The Supreme Court held that the indictment was insufficient and that Smith could not be convicted of the crime. The Court reasoned that the indictment must allege all of the essential elements of the offense in order to be valid. The Court noted that the indictment must be specific enough to inform the defendant of the charges against him and to protect him from being tried twice for the same offense. The Court concluded that the indictment in this case was insufficient because it failed to allege that the goods were stolen, which was an essential element of the offense. Therefore, the Court held that Smith could not be convicted of the crime.

In United States v. Smith, the Supreme Court was tasked with determining whether a defendant could be convicted of an offense that had been committed prior to the passage of a law making it illegal. The majority opinion held that since there was no existing law at the time of commission, conviction for such an act would violate ex post facto principles and thus be unconstitutional. Justice Field dissented from this decision on two grounds: firstly, he argued that Congress has authority to pass laws retroactively punishing acts which were not previously criminalized; secondly, he argued that even if Congress did not have such power in this case specifically, it should still be allowed because doing so would serve as a deterrent against future crimes and promote public safety. Ultimately however his dissent went unheeded and the majority opinion prevailed - conviction for offenses committed before their criminalization is prohibited under ex post facto principles.