Exclusionary rule

The exclusionary rule is a court-made remedy under which evidence gathered in violation of the Fourth Amendment, which bars unreasonable searches and seizures, is generally not admissible in a criminal trial. Related doctrines, often called "fruit of the poisonous tree," also exclude later evidence derived from the original illegality.

The Supreme Court adopted the rule for federal courts in Weeks v. United States (1914) and applied it to the states in Mapp v. Ohio (1961), part of the incorporation doctrine. Its main justification is deterrence: removing the benefit of illegal searches discourages police misconduct. The Court has created exceptions, including for evidence obtained by officers acting in good-faith reliance on a warrant later found invalid (United States v. Leon, 1984), evidence that would inevitably have been discovered, and evidence from an independent source.

Supporters say the rule is the only effective way to enforce constitutional limits on police. Critics, including some conservative jurists, argue that it lets guilty defendants go free for an officer's error and that civil lawsuits or discipline could serve instead. Its scope has narrowed in recent decades. It affects debates over police practices and civil asset forfeiture.