The Fruits of the Poisonous Tree Doctrine is a rule that was created to deter law enforcement from engaging in illegal searches and seizures. … The rule says that if any evidence is acquired by illegal means, it cannot be used against the defendant in a court of law.

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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.