What is the role of a federal magistrate in the context of search warrants?

The warrant requirement serves to interpose a "neutral and detached magistrate" between the public and the police officer, who is "engaged in the often competitive enterprise of ferreting out crime." Coolidge v. New Hampshire, 403 U.S. 443, 449, 91 S.Ct. 2022, 2029, 29 L.Ed.2d 564 (1971) (quoting Johnson v. United States, 333 U.S. 10, 14, 68 S.Ct. 367, 369, 92 L.Ed. 436 (1948)). The magistrate's independent evaluation of whether law enforcement officials have probable cause to search assures that constitutional freedoms are not infringed by zealous law enforcement efforts. See, e.g., id. at 450, 91 S.Ct. at 2029 ("[T]he whole point of the basic rule ... is that prosecutors and policemen simply cannot be asked to maintain the requisite neutrality with regard to their own investigations."); see also Steagald, 451 U.S. at 213, 101 S.Ct. at 1648. In the present case, however, a warrant issued by an American magistrate would be a dead letter in Mexico. As the district court itself recognized,

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