Note: This is an educational course, not legal advice.
If police violate the Fourth Amendment, what happens? The amendment does not say. The Court's main remedy is the exclusionary rule: evidence obtained through an unconstitutional search or seizure generally may not be used at trial to prove guilt.
Why it works
Why exclude reliable evidence? Supporters say it is the only effective deterrent to unlawful searches and keeps courts from taking part in violations. Critics, in Justice Cardozo's famous line from his time on New York's court, say "the criminal is to go free because the constable has blundered." Since the 1970s the Court has treated the rule as a deterrent, applied only where its benefits outweigh its costs. That led to exceptions.
| Exception | Case | Idea |
|---|---|---|
| Good faith | United States v. Leon (1984) | officers who reasonably relied on a warrant later found invalid; later cases extended the idea to other reasonable, good-faith mistakes |
| Independent source | the Court's cases since the 1920s | evidence also found through a separate lawful source |
| Inevitable discovery | Nix v. Williams (1984) | evidence police would have found anyway by lawful means |
| Attenuation | the Court's cases | the link between the violation and the evidence is too weak |
Key idea
Evidence from unconstitutional searches is generally excluded: Weeks (1914) in federal court, Mapp (1961) in state courts. Exceptions: good faith (Leon), independent source, inevitable discovery (Nix) and attenuation. "Fruit of the poisonous tree" (evidence derived from the violation) is excluded too, unless an exception applies.
Worked example: An invalid warrant
A judge issues a search warrant that a higher court later finds lacked probable cause. The officers had no reason to doubt it. Is the evidence excluded?
- The search violated the Fourth Amendment because the warrant was invalid.
- But under United States v. Leon, officers who reasonably relied on a warrant act in good faith, and excluding evidence would not deter police misconduct.
Answer: No; the good-faith exception applies.
Worked example: Search party
Police learn where evidence is through an unlawful interrogation, but a large search party already combing that area would have found it within hours. Admissible?
- The evidence is fruit of a violation.
- Nix v. Williams: if the government proves it would inevitably have been found by lawful means, it is admissible.
Answer: Yes; inevitable discovery.
Common mistake
Thinking an illegal search ends the case. Only the tainted evidence is excluded, the prosecution may go on with other evidence, and the exceptions often let the evidence in. The rule also does not apply in some settings, such as grand juries and civil cases.