The Fruit of the Poisonous Tree Doctrine exists to protect citizens’ Fourth Amendment rights against unlawful search and seizure. It states that directly or indirectly illegally obtained physical evidence is considered tainted, along with facts or evidence discovered later as a result of evidence obtained during the illegal search or seizure. They are, therefore, inadmissible against a defendant in a court of law.
This means that evidence obtained through illegal means taints not only the evidence, but also any facts or additional evidence later discovered by the process. What gets tainted, or violated, when police deliberately use illegal means to obtain evidence or facts is a defendant’s right to lawful search and seizure.
Picture an apple tree with some luscious apples and some diseased ruined fruits. Evidence obtained illegally can be thought of as a poison tree that is not admissible in court. This poison tree ruins some of its apples, or in other words, seriously hampers the prosecution’s case. The fruit on the poison tree could be considered bad apples, or evidence and facts gathered because of the poisoned, or illegally obtained, evidence.
Most people know that any evidence or statements obtained by means such as illegal eavesdropping or coercing the defendant will be inadmissible in court. Examples of illegal eavesdropping could be a wiretap or listening in on conversation between parties, such as using speaker phone, without their knowledge or without a legal warrant to do so. Examples of coercion include when police deliberately physically harm the person being questioned or someone important to them, or threaten or blackmail them with moral or physical harm in order to obtain incriminating information or evidence.
There is a thin line between what circumstances will and will not make specific evidence and facts admissible in a court of law.
Think back to the apples on the poison tree. Whatever is wrong with the tree that it has caused some fruits to spoil, there are other fruits its poison has not yet tainted. Like the healthy fruits ready for harvesting, there are some exceptions to this doctrine that allow evidence to be admitted even though it may have been obtained without the defendant’s consent or knowledge. For example, if a person has not been read their Miranda rights, it is not illegal for them to voluntarily make a statement they may not realize will lead police to evidence and later discovery of facts in the case.
If the evidence would have been discovered anyway without the defendant’s statement, or if the police conduct an illegal search based on good faith information, then that evidence and any facts discovered later will probably be admissible. For example, police cannot beat a suspect into telling them the location of a gun used in a crime and admit that gun as evidence at trial, but they can use the gun as evidence if it is found while searching under a legal warrant or perhaps by following a voluntary disclosure from another person.