<P> 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). </P> <P> 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 testimony of a witness who is discovered through illegal means would not necessarily be excluded, however, due to the "attenuation doctrine", which allows certain evidence or testimony to be admitted in court if the link between the illegal police conduct and the resulting evidence or testimony is sufficiently attenuated . It is believed that a witness who freely and voluntarily testifies is enough of an independent intervening factor to sufficiently "attenuate" the connection between the government's illegal discovery of the witness and the witness's voluntary testimony itself . (United States v. Ceccolini, 435 U.S. 268 (1978)) </P> <P> The "fruit of the poisonous tree" doctrine is an extension of the exclusionary rule, 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 . </P> <P> The doctrine is subject to four main exceptions . The tainted evidence is admissible if: </P>

What is the exclusionary rule and how does it relate to the fruit of the poisonous tree doctrine
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