Which case established the exclusionary rule at the federal level?

• A. Mapp v. Ohio
• B. Wolf v. Colorado
• C. Katz v. United States
• D. Weeks v. United States

Answer: (D)

The key idea is that the exclusionary rule bars using evidence obtained through unconstitutional searches and seizures in court. Weeks v. United States established this principle for federal prosecutions, ruling that items seized without a proper warrant cannot be admitted against a defendant in federal court. This set the federal-level rule that illegally obtained evidence is not admissible.

For context, later developments shaped how this applied more broadly: Wolf v. Colorado held that states weren’t yet required to follow the rule, leaving state prosecutions free to admit such evidence. Mapp v. Ohio later extended the same protection to state courts by incorporation through the Fourteenth Amendment. Katz v. United States, meanwhile, clarifies what counts as a search under the Fourth Amendment, which determines when the rule applies. But the case that first established the exclusionary rule in federal courts is Weeks.