The "fruit of the poisonous tree" doctrine is an evidentiary rule that, together with the exclusionary rule, gives the Fourth Amendment of the United States Constitution its teeth. The exclusionary rule bars illegally obtained evidence from being used in trials.
This doctrine makes certain evidence inadmissible in a trial if the primary evidence was illegally acquired. For example, you are driving and police stop you for speeding. You are clearly not impaired by drugs or alcohol, yet the police illegally search your vehicle and find a pound of marijuana in the trunk of your car.
A good criminal defense attorney should be able to have your charges dismissed because the search itself was likely illegal. It was likely an illegal search because there was no probable cause that you were under the influence of drugs or alcohol.
As with most rules, however, there are exceptions to this rule. These are:
This doctrine applies to physical evidence as well as an interrogation. For instance, during questioning by police, a suspect asks for access to a lawyer but the police ignore the request and continue with the questioning. Hours later, under duress and tired from the interrogation, the suspect winds up confessing to robbing a bank. The confession is now tainted because the police failed to stop the questioning at the right time.
The exclusionary rule allows the courts to exclude evidence at trial if it was obtained in violation of the Constitution. It usually involves Fourth and Fifth Amendment violations.
The fruit of the poisonous tree doctrine extends the exclusionary rule by excluding any evidence exposed through other evidence attained by an illegal search, seizure, or arrest.
The initial evidence obtained through a constitutional violation is the "poisonous tree." A "fruit" of that poisonous tree involves other evidence that was later discovered because of the evidence attained through the initial violation.
The fruit of the poisonous doctrine is important because it keeps prosecutors from using evidence obtained by law enforcement's illegal activities. This doctrine also helps deter negligent or reckless police misconduct.
Prior to 1914, warrantless and other shady searches conducted by law enforcement were quite common in America and evidence obtained was used against those facing criminal charges, even though the evidence was obtained illegally. However, in 1914, the U.S. Supreme Court took up the case of Weeks v. United States.
In this case, the Supreme Court created the exclusionary rule. A home belonging to the defendant was searched without a search warrant, and the evidence that was found was used to convict him of illegal gambling. The justices ruled that evidence obtained in this manner was not usable in court. The man had his conviction overturned.
In Silverthorne Lumber Co. V. United States, the exclusionary rule was extended to make evidence inadmissible if it derived from illegally obtained evidence. The phrase "fruit of the poisonous tree" was later coined in Nardone V. United States by Justice Frankfurter.
Any evidence that comes from illegal police conduct is likely inadmissible. But proving this in court will be hard, as proving it is "the fruit of the poisonous tree" is complex. An experienced criminal defense attorney will be able to present the best defense to dismiss illegally obtained evidence, which could lead to a dismissal of all charges.