The U.S. Supreme Court case Jaime Castillo, et al., v. United States in 1999 revolved around the interpretation of a federal statute that imposes mandatory minimum sentences for using or carrying a firearm during and in relation to crimes of violence or drug trafficking offenses. The defendants, Jaime Castillo and others, were charged with multiple counts related to gang activities including conspiracy to commit racketeering acts involving murder and attempted murder. They were also convicted under the aforementioned federal statute due to their use of firearms during these criminal activities. The issue before the court was whether this law applied only when the defendant actively used a firearm or if it could be extended to situations where they merely possessed one while committing another crime. The defendants argued that mere possession did not constitute "use" as per statutory language. However, the Supreme Court ruled against them by interpreting “use” broadly enough so as not just active employment but also encompassing possession which facilitates an underlying crime even without actual discharge of weapon involved in those crimes. This decision upheld their convictions and affirmed lower courts' rulings on applying enhanced penalties for gun possession during violent crimes or drug trafficking offenses.

In the dissenting opinion for Jaime Castillo, et al., v. United States (1999), Justice O'Connor disagreed with the majority's interpretation of 18 U.S.C. §924(c). She argued that Congress intended to create a separate offense for using or carrying a firearm during and in relation to any crime of violence or drug trafficking crime, and another distinct offense for possessing a firearm in furtherance of such crimes. The distinction between these offenses was based on whether the defendant actively employed the weapon versus merely possessed it. According to her view, this interpretation would better align with Congressional intent by ensuring harsher penalties only applied when firearms were actively used in criminal activities rather than simply being present at the scene. Therefore, she believed that defendants should be charged separately depending on their specific involvement with firearms during their crimes.