The exclusionary rule prevents the government from using most evidence gathered in violation of the United States Constitution. The exclusionary rule applies to evidence gained from an unreasonable search or seizure in violation of the Fourth Amendment, see Mapp v. Ohio, 367 U.S. 643 (1961), to improperly elicited self-incriminatory statements gathered in violation of the Fifth Amendment, see Miranda v. Arizona, 384 U.S. 439 (1966), and to evidence gained in situations where the government violated defendants’ Sixth Amendment right to counsel, see Miranda. The rule does not apply in civil cases, including deportation hearings. See INS v. Lopez-Mendoza, 468 U.S. 1032.
If evidence that falls within the scope of the exclusionary rule led law enforcement to other evidence, which they would not otherwise have located, then the exclusionary rule applies to the related evidence found subsequent to the excluded evidence, subject to a few exceptions. Such subsequent evidence is called “fruit of the poisonous tree.”
The exclusionary rule is a court-created remedy and deterrent, not an independent constitutional right. The purpose of this rule is to deter law enforcement officers from conducting searches or seizures in violation of the Fourth Amendment and provide remedies to defendants whose rights have been infringed upon. Courts have also carved out several exceptions to the exclusionary rule where the costs of exclusion outweigh its deterrent or remedial benefits. Thus, the rule is not triggered when courthouse errors lead police officers to mistakenly believe that they have a valid search warrant, because excluding the evidence would not deter police officers from violating the law in the future.
GOOD FAITH EXCEPTION
Under the good-faith exception, evidence is not excluded if it is obtained by officers who reasonably rely on a search warrant that turns out to be invalid. See Arizona v. Evans, 514 U.S. 1 (1995). Also in Davis v. U.S.131 S.Ct. 2419 (2011), the Supreme Court ruled that exclusionary rule does not apply when the police conduct a search when relying on binding appellate precedent. Evidence may also be admissible if the officers rely on an invalid statute. In Herring v. U.S., 555 U.S. 135 (2009), the Court found that the good-faith exception to the exclusionary rule applies when police employees erred in maintaining records in a warrant database.
INDEPENDENT SOURCE DOCTRINE
Evidence initially obtained during an unlawful search or seizure may later be admissible if the evidence is later obtained through a constitutionally valid search or seizure. See. Maryland v. Macon. 472 U.S. 463 (1985).
INEVITABLE DISCOVERY DOCTRINE
EVIDENCE ADMISSIBLE FOR IMPEACHMENT
The exclusionary rule does not prevent the government from introducing illegally gathered evidence to “impeach,” or attack the credibility of, defendants’ testimony at trial. The Supreme Court recognized this exception to prevent perjury. Even when the government suspects perjury, however, it may only use tainted evidence for impeachment, and may not use it to show guilt.
Due to qualified immunity, the exclusionary rule is often defendants’ only remedy when police officers conduct an unreasonable search or violate their Miranda rights. Even if officers violate a defendant's constitutional or statutory rights, qualified immunity protects them from a lawsuit unless no reasonable officer would believe that their conduct was legal.