What prevents illegally obtained evidence from being used in criminal trials?

The correct answer is the exclusionary rule, which is a fundamental principle in the U.S. legal system. This rule prohibits the use of evidence that has been obtained in violation of a defendant's constitutional rights, particularly the Fourth Amendment, which protects against unreasonable searches and seizures. The purpose of the exclusionary rule is to deter law enforcement from conducting illegal searches and to uphold the integrity of the judicial process.

By excluding improperly obtained evidence, the rule helps to ensure that justice is administered fairly and that individuals' rights are respected. This means that if law enforcement officers obtain evidence without a proper search warrant or without probable cause, that evidence cannot be used in court against the accused.

The other options, while relevant in their own contexts, do not serve the same purpose as the exclusionary rule. The search warrant requirement establishes the need for judicial approval before conducting a search, but it is the exclusionary rule that specifically addresses the consequences of failing to follow that requirement. The double jeopardy clause protects individuals from being tried twice for the same crime, and the hearsay rule pertains to the admissibility of secondhand testimony, neither of which relates directly to the issue of illegally obtained evidence.