In Spinelli v. United States, the U.S. Supreme Court ruled on a case involving the Fourth Amendment's protection against unreasonable searches and seizures. The court held that an informant’s tip could not be considered probable cause for issuing a search warrant unless it was accompanied by some supporting evidence or circumstances indicating its reliability and credibility. In this case, FBI agents had obtained a search warrant based solely on an anonymous letter claiming that defendant Spinelli was running illegal gambling operations from his home in St Louis, Missouri. During their subsequent search of his residence, they found incriminating evidence which led to his conviction for interstate transmission of wagering information (a federal crime). However, the Supreme Court overturned this verdict because there were no corroborating details provided about how the informant knew about Spinelli's alleged criminal activities nor any independent verification made by law enforcement before obtaining their warrant.

In the dissenting opinion for Spinelli v. United States, Justice White argued that the majority's decision to overturn Spinelli's conviction was based on an overly rigid interpretation of probable cause and failed to give due weight to law enforcement expertise. He contended that while anonymous tips should be treated with caution, they could still contribute valuable information towards establishing probable cause when corroborated by independent police work or other sources of information. In this case, he believed there was sufficient corroboration through surveillance and a check into Spinelli’s criminal record which confirmed his involvement in illegal gambling activities in the past. Furthermore, he criticized the majority for not considering all relevant factors holistically but instead dissecting each piece of evidence separately before dismissing it as insufficient proof of wrongdoing. This approach according to him undermined effective policing and set unrealistic standards for obtaining search warrants.