The Warren Court had decided a pair of cases, Aguilar v. Texas (1964) and Spinelli v. United States (1969) that made the warrant requirement tougher for police when they relied on confidential informants. Under the Aguilar-Spinelli test, an informant’s tip can furnish probable cause for an arrest if the State establishes (1) the basis of the informant’s information and (2) the credibility of the informant or the reliability of the informant’s information.

The Burger Court changed this in its 1983 decision Illinois v. Gates when it abandoned the Aguilar-Spinelli test in favor of a more deferential totality of the circumstances test. Under this test, the Court wrote: “The task of the issuing magistrate is simply to make a practical, common-sense decision whether, given all the circumstances set forth in the affidavit before him, including the veracity and basis of knowledge of persons supplying hearsay information, there is a fair probability that contraband or evidence of a crime will be found in a particular place.”