In the 1980 case Mariscal v. United States, the Supreme Court ruled on an appeal by a defendant convicted of smuggling marijuana into the country from Mexico. The defendant argued that his constitutional rights were violated when he was not allowed to cross-examine a government informant who had provided crucial evidence against him but did not testify at trial due to being in federal protective custody. The court held that while defendants generally have a right to confront their accusers, this right is not absolute and can be limited if there are compelling reasons for doing so. In this case, it found that protecting the safety of informants could justify limiting cross-examination under certain circumstances and upheld the conviction.

In the dissenting opinion for Mariscal v. United States, it was argued that the majority's decision to uphold a warrantless search of a private residence based on exigent circumstances was flawed. The dissenting justices believed that there were no immediate threats or dangers present at the time of the search which could justify bypassing Fourth Amendment protections against unreasonable searches and seizures. They contended that police officers had ample opportunity to secure a warrant before conducting their search but chose not to do so, thus violating constitutional rights. Furthermore, they disagreed with the majority's view that evidence obtained during this unlawful search should be admissible in court under an exception to exclusionary rule doctrine known as "good faith" reliance on existing law by law enforcement officials. In their view, allowing such evidence would undermine citizens' privacy rights and incentivize future violations by police.