## Facts

- The FBI sought a warrant to search a St. Louis apartment as part of an investigation of illegal gambling activities.
- An FBI agent submitted an affidavit stating that agents observed William Spinelli repeatedly travel from Illinois into St. Louis and park at an apartment building; on one occasion he entered a specified apartment.
- The affidavit identified two telephone numbers assigned to the apartment and asserted Spinelli was known to the affiant as a gambler and associate of gamblers.
- The affidavit also reported that a “confidential reliable informant” said Spinelli was operating a bookmaking operation and using the identified telephones to accept wagers and disseminate wagering information.
- Evidence seized during the apartment search was central to Spinelli’s conviction under 18 U.S.C. § 1952.
- After the court of appeals ultimately upheld the warrant, the Supreme Court granted review limited to the Fourth Amendment validity of the search and seizure.

## Issues

1. Whether the affidavit supporting the search warrant established probable cause under the Fourth Amendment when it relied substantially on an informant’s tip.
2. Whether police corroboration of neutral details (travel, apartment entry, telephone subscriptions) can cure an informant tip that lacks sufficient factual support for credibility and basis of knowledge.

## Decision

- The Supreme Court reversed and remanded.
- The Court held the affidavit did not establish probable cause because the informant’s tip was insufficient under the standards governing hearsay-based warrants.
- The Court concluded that corroboration of limited, noncriminal details did not supply the missing showing that the tip was reliable or based on adequate underlying circumstances.

## Legal Principles

- When a warrant affidavit relies on an informant’s hearsay, it must provide enough facts for a magistrate to make an independent probable-cause determination rather than accept conclusory police assertions.
- Under the Aguilar framework, the affidavit must (1) state underlying circumstances showing how the informant obtained the information (basis of knowledge) and (2) provide a factual basis to credit the informant’s reliability or credibility (veracity).
- Characterizations such as “reliable informant” or “known gambler,” without supporting facts, are inadequate to establish probable cause.
- Corroboration of innocent or routine conduct may confirm identity or location but does not, by itself, establish a fair probability of criminal activity when the tip otherwise lacks detail indicating illegal conduct.
- A sufficiently detailed tip may be credited when its specificity and predictive content support an inference of personal knowledge, but a general accusation of wrongdoing without supporting particulars does not.

## Conclusion

The Court held that the warrant was invalid because the affidavit’s informant tip failed to provide the necessary underlying facts showing reliability and basis of knowledge, and the FBI’s corroboration of innocuous details did not transform the affidavit into probable cause; therefore, the search violated the Fourth Amendment and the conviction could not stand on the seized evidence.


Spinelli v. United States, 393 U.S. 410 (1969)