The judicial branch resolves legal disputes and interprets rules created by the legislative and executive branches.
Court opinions that address issues not explicitly covered by existing statutes can stand as an independent source of legal rules (known as "common law").
Sloan, Amy E. (2015). Basic Legal Research: Tools and Strategies (6th ed.). New York: Wolters Kluwer, p. 7
There are several resources that can provide you with access to federal court opinions that may relate to your research topic.
Westlaw allows you to perform more targeted searches by limiting your results to a particular district court or federal circuit.
One of the database's greatest features is the KeyCite system, which finds connections ot other cases, statutes, and regulations and even summarizes the nature of the treatment presented in the rest of the law.