In the case of Smith v. United States in 1976, the Supreme Court ruled on a matter involving federal jurisdiction over crimes committed on Native American reservations. The defendant, an enrolled member of the Navajo Tribe, was charged with committing a crime within "Indian country" as defined by U.S law but argued that his actions took place outside this area and thus should not be subject to federal jurisdiction. However, based on evidence presented at trial showing that the crime occurred within reservation boundaries established by Congress in 1868 and never subsequently diminished or disestablished, it was determined that he had indeed acted within Indian country. Therefore, his conviction for assault resulting in serious bodily injury under applicable federal law was upheld unanimously by all nine justices.

In the dissenting opinion for Smith v. United States, Justice Marshall argued that the majority's decision to uphold a conviction based on an ambiguous statute was incorrect. He believed that ambiguity in criminal statutes should be interpreted in favor of defendants, not against them - a principle known as the rule of lenity. This is because individuals have a right to fair notice about what conduct is criminally punishable and also because it’s Congress’ responsibility to define criminal liability clearly. In this case, he felt there was reasonable doubt whether transporting stolen goods 'in interstate commerce' included acts after transportation had ended (i.e., selling those goods). Therefore, he would have reversed Smith's conviction for selling stolen property across state lines under federal law.