What is the "good faith" exception to a finding that a search warrant was invalid for lack of probable cause?

Since Sergeant Rullamas's conclusion was reasonable, the subsequent execution of a facially valid warrant, issued by a neutral magistrate, was done in good faith. Therefore, even if the warrant was invalid for lack of probable cause, its execution was nonetheless proper. (Massachusetts v. Sheppard (1984) 468 U.S. 98l, 987-988.)

We conclude that the "good-faith" exception applies. Thus, even assuming defense counsel should have challenged the sufficiency of the probable cause supporting the search warrant, the searching officers acted in good faith on what appeared to be a facially valid warrant signed by a neutral magistrate. (United States v. Leon, supra, 468 U.S. at p. 923.) Accordingly, defense counsel cannot be faulted for failing to file a futile motion.