Fruit of the Poisonous Tree

Fruit of the poisonous tree is a legal metaphor in the United States used to describe evidence that is obtained illegally.  The logic of the terminology is that if the source (the "tree") of the evidence or evidence itself is tainted, then anything gained (the "fruit") from it is tainted as well. The fruit of the poisonous tree doctrine was first described in Silverthorne Lumber Co. v. United States, 251 U.S. 385 (1920).  The term's first use was by Justice Felix Frankfurter in Nardone v. United States (1939).

Such evidence is not generally admissible in court.  For example, if a police officer conducted an unconstitutional (Fourth Amendment) search of a home and obtained a key to a train station locker, and evidence of a crime came from the locker, that evidence would most likely be excluded under the fruit of the poisonous tree legal doctrine. The discovery of a witness is not evidence in itself because the witness is attenuated by separate interviews, in-court testimony and his or her own statements.

The doctrine is an extension of the exclusionary rule [see below], which, subject to some exceptions, prevents evidence obtained in violation of the Fourth Amendment from being admitted in a criminal trial. Like the exclusionary rule, the fruit of the poisonous tree doctrine is intended to deter police from using illegal means to obtain evidence.

The doctrine is subject to four main exceptions. The tainted evidence is admissible if:

1. it was discovered in part as a result of an independent, untainted source; or
2. it would inevitably have been discovered despite the tainted source; or
3. the chain of causation between the illegal action and the tainted evidence is too attenuated; or
4. the search warrant was not found to be valid based on probable cause, but was executed by government agents in good faith (called the good-faith exception).

This doctrine was also used by the European Court of Human Rights in Gäfgen v. Germany. In certain cases continental European countries have similar laws (e.g. in cases of torture), while the doctrine itself is generally not known. Illegally obtained evidence is used by the courts to ensure that the judgment is factually correct, however the person obtaining the illegal evidence typically faces independent consequences.

https://en.wikipedia.org/wiki/Fruit_of_the_poisonous_tree

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Exclusionary Rule

The exclusionary rule is a legal principle in the United States, under constitutional law, which holds that evidence collected or analyzed in violation of the defendant's constitutional rights is sometimes inadmissible for a criminal prosecution in a court of law. This may be considered an example of a prophylactic rule formulated by the judiciary in order to protect a constitutional right. The exclusionary rule may also, in some circumstances at least, be considered to follow directly from the constitutional language, such as the Fifth Amendment's command that no person "shall be compelled in any criminal case to be a witness against himself" and that no person "shall be deprived of life, liberty or property without due process of law".

"The exclusionary rule is grounded in the Fourth Amendment and it is intended to protect citizens from illegal searches and seizures."  The exclusionary rule is also designed to provide a remedy and disincentive, which is short of criminal prosecution in response to prosecutors and police who illegally gather evidence in violation of the Fifth Amendment in the Bill of Rights compelled to self-incrimination. The exclusionary rule also applies to violations of the Sixth Amendment, which guarantees the right to counsel.

Most states also have their own exclusionary remedies for illegally obtained evidence under their state constitutions and/or statutes, some of which predate the federal constitutional guarantees against unlawful searches and seizures and compelled self-incrimination.

This rule is occasionally referred to as a legal technicality because it allows defendants a defense that does not address whether the crime was actually committed. In this respect, it is similar to the explicit rule in the Fifth Amendment protecting people from double jeopardy. In strict cases, when an illegal action is used by police/prosecution to gain any incriminating result, all evidence whose recovery stemmed from the illegal action—this evidence is known as "fruit of the poisonous tree"—can be thrown out from a jury (or be grounds for a mistrial if too much information has been irrevocably revealed).

The exclusionary rule applies to all persons within the United States regardless of whether they are citizens, immigrants (legal or illegal), or visitors.

https://en.wikipedia.org/wiki/Exclusionary_rule