Aguilar v. Texas
In Aguilar v. Texas, 378 U.S. 108, 84 S.Ct. 1509, 12 L.Ed.2d 723 (1964), the Court established a two prong test which must be met when probable cause is based upon information provided by an unidentified informant:
The magistrate must be informed of some of the underlying circumstances from which the informant concluded that the narcotics were where he claimed they were, and some of the underlying circumstances from which the officer concluded that the informant, whose identity need not be disclosed, was "credible" or his information "reliable." Id. at 112, 84 S.Ct. at 1512.