Within the United States federal and state judiciary hierarchy, case law research requires that the final answer contains the decision from the court of last resort. Within this logic, the United States Supreme Court decisions are seldom overruled by the Court or questioned by Congress in subsequent legislation.

To the extent the content of its decisions corresponds to our contemporary values, and the Court exercises publicly justifiable power, those decisions constitute the law of the land.

More abstractly, “the rule of law” relies on those court decisions, and more problematically, they are never discarded, even when they may be a statutory interpretation violating the very essence of the statute they are applying. In fact, the Court's decision assigns meaning for all practical purpose to a statute.

For example, in 1990, Congress passed the Gun-Free School Zones Act of 1990, which declared it unlawful for any individual to posses a firearm in a school zone. Congress limited the offense to the type of firearm. In Section 922(j)(2)(A), Congress stated that:

  • It shall be unlawful for any individual knowingly to possess a firearm that has moved in or that otherwise affects interstate or foreign commerce at a place that the individual knows, or has reasonable cause to believe, is a school zone.

Alfonso Lopez., a 12th-grade student, who went to Edison High School in San Antonio, Texas, carrying a concealed .38-caliber handgun and five bullets, was charged with violating the statute. He challenged the federal statute’s constitutionality, and filed a lawsuit in the appropriate federal court. The U.S. Supreme Court accepted to review the circuit decision, by granting a writ of certiorari. The Court held that Congress did not have the authority to make firearms’ possession a federal offense. In deciding the case—whose title became United States v. Lopez, 514 U.S. 549 (1995) after the name of the parties involved—the Court ignored the provision underlined above and held that:

  • The Act neither regulates a commercial activity nor contains a requirement that the possession be connected in any way to interstate commerce. We hold that the Act exceeds the authority of Congress “[t]o regulate Commerce ... among the several States.”

The Court did not see any specific commercial qualification on the type of firearm involved, although it may reasonably be argued to the contrary. While subsequent bills to reauthorize the ban on undetectable firearms were introduced in the House in 2004, the statutory provisions of the Gun-Free School Zones Act of 1990 continue to remain unconstitutional and thus not binding. When the Supreme Court decides the unconstitutionality of a statute, the only recourse is for Congress to address that finding by passing another statute that incorporates the Court’s suggestion.

In conclusion, with Lopez, the Court altered both the statutory meaning of a specific act of Congress, the Gun-Free School Zones Act of 1990 (later amended to incorporate the Court's decision), but also a Constitutional provision, the Commerce Clause. This specific example, shows how statutory research cannot stop with the applicable act, and in addition, in cannot stop with the trial case applying it.

The correct and comprehensive answer to any statutory and case law research question has to include the related decision from the court of last resort. If the researched issue is a state issue, then the court of last resort is that state's (most often) supreme court. If the researched issue is a federal issue, then the court of last resort is the United States Supreme Court, which is often referred to as the Court.

In addition, remember that sometimes the Court may decide not to follow its own precedents and it will reverses itself. As a result, while apparently rarely necessary, you still need to update and check the status of your research of Supreme Court decisions as well, looking for the most recent Court decision on your research topic.