It has been 84 years since Judge Benjamin Cardozo eloquently summarized the strong opposition to the federal exclusionary rule adopted by the U.S. Supreme Court 12 years earlier: “The criminal is to go free because the constable has blundered.”1 Cardozo would have been pleased to learn, however, that not every “blunder” has resulted in the exclusion of evidence. A number of recent cases have demonstrated that reasonable mistakes of fact are generally tolerated under the Fourth Amendment. On the other hand, a police officer’s mistake of law will not be excused. This column will discuss the difference between the two types of errors and why the distinction is not always easy to discern.
Mistake of Law
A mistake of law occurs when a police officer’s conduct is based upon the officer’s erroneous understanding or belief of the law. Such error, no matter how reasonable, will not be excused.2 A mistaken belief in the law can be based on an officer’s misunderstanding or misreading of a statute, a failure to learn that the law has been changed, or an unfamiliarity with the law itself. Errors of law cannot be excused because, to do so, “would provide a strong incentive to police officers to remain ignorant of the language of the laws that they enforce and of the teachings of the judicial decisions whose principal function frequently is to construe such laws and to chart the proper limits of police conduct.”3 On the other hand, a police officer will be excused if his actions were based on a mistaken, but reasonable, view of the facts.
