Which principle ensures that evidence obtained through illegal conduct is inadmissible?

The principle that ensures evidence obtained through illegal conduct is inadmissible is known as the exclusionary rule. This legal doctrine prohibits the use of evidence in court if it was gathered in violation of a defendant's constitutional rights, particularly under the Fourth Amendment, which protects against unreasonable searches and seizures. When evidence is gathered through illegal means, it fundamentally undermines the fairness of the judicial process, and the exclusionary rule serves as a deterrent against illegal police conduct.

While "fruit of the poisonous tree" specifically refers to the idea that any evidence derived from an illegal search or seizure (the "poisonous tree") is also inadmissible (the "fruit") in court, the broader principle in the question focuses on the exclusionary rule itself. Thus, the correct choice highlights the overarching principle that encompasses this concept of inadmissibility due to illegal conduct in gathering evidence.