Here’s an important, ominously named legal rule-

Fruit of the Poisonous Tree Doctrine: This cleverly named principle works within the exclusionary rule in the United States. The exclusionary rule prohibits the use of illegally obtained evidence in a criminal trial.

The idea is, evidence tainted by an unconstitutional action (the “poisonous tree”) must be excluded from trial, along with all evidence derived from it (the “fruit”).

(Example – during an illegal search a gun is found. They also find a bill for a storage unit. The unit is searched and drugs are found.  The drugs are the ‘fruit’ and thus not admissible in court.)

The Fruit of the Poisonous Tree doctrine serves to prevent unlawful police conduct by discouraging them from engaging in unconstitutional searches & seizures. It’s purpose is to protect individuals’ Fourth Amendment rights by ensuring evidence obtained in violation of those rights is not used against them in court.