The “Fruit of the Poisonous Tree Doctrine” is a famous evidentiary legal doctrine that has been publicized on television and in the movies. This doctrine is based upon “The Exclusionary Rule”, an important evidence doctrine that requires that the victim of an illegal search or a coerced confession can have the product of the illegality excluded from criminal prosecution. This exclusionary rule has certain limitations: 1) Impeachment: The evidence can be used for impeachment purposes even if obtained in violation of the Constitution. It can be used only to impeach the trial testimony of the defendant, not that of other witnesses; 2) The exclusionary rule does not apply to grand jury hearings, civil proceedings, or parole revocation hearings; 3) In order for the exclusionary rule to apply there has to be a federal nexus (meaning a violation of the Constitution or Federal Statute). 4) The good faith exception to the exclusionary rule (known as the Leon doctrine): Even if the evidence was obtained in violation of the defendant’s constitutional rights, if the police operated in good faith, the good faith doctrine trumps the exclusionary rule. Examples of the good faith doctrine are the police relying on a judicial opinion that is later overturned or a good faith reliance on a defective search warrant.
If the exclusionary rule applies then the “fruit of the poisonous tree” doctrine may also apply. If the exclusionary rule is applied at trial, not only all evidence that is illegally obtained is excluded, but also all evidence derived from the illegal evidence will also be excluded as “fruit of the poisonous tree”. There are a few exceptions to this doctrine as well: 1) If the constitutional violation is a failure to give Miranda warnings then physical fruits obtained because of this failure are not excluded (known as an unwarned but voluntary statement); 2) If the authorities can “purge the taint” from the violation of a constitutional right and restore free will then the “fruit of the poisonous tree doctrine” does not apply. This can be done in three ways: a) The Independent Source doctrine: the evidence was obtained illegally but there was another independent source to obtain the evidence constitutionally; b) The Inevitable Discovery doctrine: The police would have found the illegally obtained evidence anyway even absent the constitutional violation; c) The Attenuation doctrine: There were intervening acts between the illegality and the illegally obtained evidence that restored free will. If none of these exceptions to the “fruit of the poisonous tree doctrine” apply, then the illegally obtained evidence will be excluded under the exclusionary rule and any evidence derived therefrom will also be excluded under the “fruit of the poisonous tree” doctrine.