What is the test for establishing probable cause for a search warrant?

The Fourth Amendment requirement that probable cause be shown for a warrant to issue means, in essence, that the magistrate must be presented with information as to facts or circumstances sufficient to give him, as a reasonable person, grounds to believe that a crime is being or has been committed. Generally a court that is assessing whether probable cause was shown must look only to the information that was before the magistrate; a suppression hearing may not be used to bring out information on the basis of which the warrant could have issued, but which was not presented to the magistrate. United States v. Menser, 360 F.2d 199, 203 (2d Cir. 1966). But the task of the court here was not, in the first instance, to assess the probative value or sufficiency of the information presented. It was to determine what information that was presented to the magistrate should not have been presented. It is entirely appropriate for the court, on a proper showing by the defendant, ¹³ to hold a suppression hearing to determine which information that had been presented was in fact tainted. Thereafter the court must decide whether the untainted information that was presented to the magistrate, considered by itself, sufficed to establish probable cause. ¹⁴ If the untainted information alone established probable cause, the evidence seized pursuant to the warrant should not be suppressed: