We have frequently questioned whether the exclusionary rule can have any deterrent effect when the offending officers acted in the objectively reasonable belief that their conduct did not violate the Fourth Amendment. [. . .] But even assuming that the rule effectively deters some police misconduct and provides incentives for the law enforcement profession as a whole to conduct itself in accord with the Fourth Amendment, it cannot be expected, and should not be applied, to deter objectively reasonable law enforcement activity.
Good Faith Quote: Leon
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This is particularly true, we believe, when an officer, acting with objective good faith, has obtained a search warrant from a judge or magistrate and acted within its scope. In most such cases, there is no police illegality, and thus nothing to deter. It is the magistrate's responsibility to determine whether the officer's allegations establish probable cause and, if so, to issue a warrant comporting in form with the requirements of the Fourth Amendment. In the ordinary case, an officer cannot be expected to question the magistrate's probable cause determination or his judgment that the form of the warrant is technically sufficient. "[O]nce the warrant issues, there is literally nothing more the policeman can do in seeking to comply with the law." Id. at 498 (BURGER, C.J., concurring). Penalizing the officer for the magistrate's error, rather than his own, cannot logically contribute to the deterrence of Fourth Amendment violations.
United States v Leon, 468 US 879 (1984) (internal quotation and citations omitted)