393 U.S. 410 (1969)
Spinelli v. United States is a landmark case in the realm of search and seizure law, primarily focusing on the use of informant tips to establish probable cause for the issuance of a search warrant.
Does an affidavit that relies on a confidential informant's tip satisfy the Fourth Amendment's probable cause requirement if it lacks detailed information about the informant's reliability and the basis of their knowledge?
The two-prong test for informant tips requires that (1) the affidavit provide underlying circumstances from which the informant gathered their information, and (2) the affidavit contains some evidence of the informant's reliability or credibility.
The Supreme Court held that the affidavit in Spinelli's case did not meet the two-prong test established in Aguilar v. Texas. It lacked sufficient detail to demonstrate the informant's credibility and the basis of his knowledge, thereby failing to establish probable cause under the Fourth Amendment.
Spinelli v. United States is significant for its elaboration on the two-prong test concerning informant tips and probable cause. The refinement and application of the test in this case provided clearer guidance for law enforcement and lower courts on the requirements needed for issuing search warrants based on informant information. For law students, this decision is crucial to understanding the practical limitations on secretive information in criminal procedure and the careful judicial balancing of public safety and individual rights.