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Illinois v. Gates

Citation. 462 U.S. 213, 103 S. Ct. 2317, 76 L. Ed. 2d 527 (1983)
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Brief Fact Summary.

The police received an anonymous letter outlining specific details about the Defendants, Gates and others (the “defendants”), plans to traffic drugs from Florida to Illinois. When the details were corroborated by the defendants’ actions, police obtained a search warrant and found drugs, weapons and other contraband in the defendants’ home and automobile.

Synopsis of Rule of Law.

Where an anonymous tip is corroborated with actual police findings, a “totality of the circumstances” approach is an appropriate way of determining probable cause instead of using the two-pronged test of “veracity/reliability” and “basis of knowledge” from Spinelli v. United States, 393 U.S. 410 (1969). The Fourth Amendment of the United States Constitution (“Constitution”) requires no more than a finding by an issuing magistrate that there is a “substantial basis” that a search will uncover evidence of wrongdoing.


The police received a highly detailed anonymous tip that the defendants were trafficking drugs. The police, following up on the tip, observed the defendants conducting specific activities which were outlined in the tip. On the basis of the tip and the defendants’ corroborating activities, the police obtained a search warrant. Upon execution of the warrant, the police found drugs, weapons and other contraband in the defendants’ automobile and home.


May a magistrate issue a valid warrant on the basis of an anonymous tip where there is no indicia of the informer’s “basis of knowledge” if the information contained in the tip is corroborated with police findings?


When a court decides whether or not to issue a search warrant, the elements of the informant’s “credibility/reliability” and “basis of knowledge” are to be used as guides when considering the “totality of the circumstances” and are not to be exclusive requirements applied in every case.


Aguilar and the elaboration in Spinelli sets forth the analysis magistrates should follow on determinations of probable cause. To sufficiently uphold Fourth Amendment rights, magistrates must look at both the “credibility/reliability” and “basis of knowledge” of the informant. “Basis of knowledge” cannot fully be supported solely on the basis that some factual assertions corroborate with actual police findings.
Since some of the anonymous tips were not corroborated and actually proved false, the informant’s “credibility/reliability” was undermined and therefore the warrant should not have been issued. Police cannot use findings of an illegal search to substantiate a previously issued warrant.

Concurrence. Even if the factual findings by police were only corroborated by innocuous behavior, a valid warrant could still have been issued because the defendants’ actions were suspicious. The main focus should be whether there is an inference, based upon the suspects’ actions, that the informant is credible and the information was obtained in a reliable manner.


“Credibility/reliability” and “basis of knowledge” of an informant are very relevant in determining the value of a tip. These elements alone do not form the entire basis of inquiry in deciding whether probable cause exists. So long as the magistrate had a substantial basis for concluding a search would uncover evidence of wrongdoing, the Fourth Amendment is not violated.

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