Final answer:
The exclusionary rule from Weeks v. United States and Mapp v. Ohio, makes evidence obtained in violation of the Fourth Amendment inadmissible in state courts, which includes any subsequent evidence considered 'fruit of the poisonous tree.'
Step-by-step explanation:
The exclusionary rule established by the Supreme Court cases Weeks v. United States and Mapp v. Ohio dictates that evidence obtained in violation of the Fourth Amendment, which guards against unreasonable searches and seizures, is not admissible in state courts. If the police conduct a search or seizure without a warrant, and it does not fall under specific exceptions, any evidence found cannot be used in court. This also extends to evidence that is subsequently discovered as a result of the unlawful search, known as the 'fruit of the poisonous tree.' However, there are exceptions to this rule, such as when police believe they have a valid warrant ('good faith' exception) or when the evidence would have inevitably been discovered legally ('inevitable discovery' exception).