Final answer:
Evidence that may not be used against a defendant in a criminal trial because it was obtained illegally is an example of the exclusionary rule. The exclusionary rule is a principle that disallows the use of evidence in court that was obtained in violation of constitutional rights, specifically against unreasonable searches and seizures as protected by the Fourth Amendment.
Step-by-step explanation:
Evidence that may not be used against a defendant in a criminal trial because it was obtained illegally is an example of the exclusionary rule. The exclusionary rule is a legal principle in the United States, mandating that evidence collected or analyzed in violation of the defendant's constitutional rights is sometimes inadmissible for a criminal prosecution in a court of law. This rule is grounded in the Fourth Amendment, which protects against unreasonable searches and seizures and is designed to preserve the integrity of the criminal justice system by discouraging unlawful conduct by law enforcement.
Notably, there are some exceptions to the exclusionary rule—such as the "good faith" exception and the "inevitable discovery" exception—however, the core idea is that evidence obtained from an unconstitutional search or seizure cannot be used against a person in court. The idea is encapsulated in the concept of "fruit of the poisonous tree," where not only is the directly obtained evidence considered tainted, but also any subsequent evidence that is derived from the initial illegal search or seizure. This concept was established in landmark Supreme Court cases such as Mapp v. Ohio and Weeks v. United States.
Hearsay evidence, direct evidence, and circumstantial evidence, on the other hand, are different classifications of evidence that can be used in a trial under the right circumstances and do not inherently involve constitutional violations as does evidence barred by the exclusionary rule.