Fruit of the poisonous tree
Fruit of the poisonous tree is a legal theory in the United States that makes illegally obtained evidence, as well as subsequent evidence legally obtained if discovered solely as a result of the illegally obtained evidence, inadmissible in a court of law. It is also called the exclusionary rule. In the United States, defendants may make a motion to suppress such evidence, which means that the defendant is asking the trial judge to rule such evidence inadmissible during his or her trial.
For example, if a suspect has a confession beat out of him, and during the course of that confession, details to authorities to the location of a victim's body, and the authorities obtain a search warrant and recover the body, neither the confession nor the body can be used against the suspect in criminal proceedings, unless the police can show that a) it was inevitable that the body would have been discovered anyways, b) that an independent source, such as a witness, had informed them of where the body was, or c) the connection between the illegally obtained evidence and the subsequently discovered evidence was so weakened or stretched as to remove the "taint" of illegality.
The fruit of the poisonous tree doctrine is related to the exclusionary rule, which finds its origins in Weeks v. United States 232 U.S. 383 (1914), a case argued before the Supreme Court on December 2-3, 1913, and ultimately, the Bill of Rights. In Weeks v. United States, Justice William R. Day overturned Weeks's conviction because the evidence used against him at trial was obtained in violation of the Fourth Amendment, and ruled that the illegally obtained evidence could not be used against Weeks.
The exclusionary rule came about as a remedy for violations of suspects constitutional rights. However, some argue that it is ridiculous that a crimminal go free "because the constable blundered." While other remedies are conceivable, such as holding both the constable and the suspect accountable for their own actions and violations, in the United States, the exclusionary rule remains judicial precedent.