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 of the evidence (the "tree") is tainted, then anything gained from it (the "fruit") is tainted as well. The term fruit of the poisonous tree was first used in Nardone v. United States in the opinion by Justice Felix Frankfurter.

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 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, 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 not based on probable cause was executed by government agents in good faith (called the good faith exception).

The fruit of the poisonous tree doctrine stems from the 1920 case of Silverthorne Lumber Co. v. United States.