The good faith exception doctrine is an exception to the exclusionary rule provides that illegally gathered evidence can be admitted at trial if police officers have reason to believe their actions are legal. Under the original exclusionary rule, police were strictly responsible for their violations of constitutional law. The good faith rule permits the courts to consider the mental state of the police officer.
So far the new rule has been confined to errors made by judges or legislatures. If the judge, for example, makes a mistake in issuing a warrant, the police officer is not responsible if she had good reason to believe that the warrant was valid. The rationale for this change is that the exclusionary rule is designed, as a last resort, to punish police for misconduct. When judges and legislatures make mistakes, the higher courts have methods of correcting them, so rationale behind the exclusionary rule is inapplicable.