Aguilar v. Texas

In determining the validity of a search warrant, a reviewing court may consider only the information brought to a magistrate’s attention. A requesting officer must establish facts for a magistrate judge to consider whether probable cause exists or not. The Fourth Amendment does not deny law enforcement the support of usual inferences that reasonable persons may draw from evidence. It does, however, require such inferences be drawn by a neutral and detached magistrate instead of an officer engaged in the competitive enterprise of ferreting out crime.

An affidavit for a search warrant may be based on hearsay information and need not reflect direct personal observations of the affiant. But the magistrate must be informed of some of the underlying circumstances on which the informant based conclusions and some of the underlying circumstances from which an officer concluded that the informant, whose identity need not be disclosed, was “credible” or that his information was reliable. Although the reviewing court will grant substantial deference to judicial determinations of probable cause, the court must still insist that the magistrate perform a “neutral and detached” function and not serve merely as a “rubber stamp.”