Ms. Mapp was convicted of possessing obscene materials, even though the evidence was taken without a warrant. She was tried in state court, like the overwhelming majority of criminal defendants. So it did her no good that federal courts had applied the so-called “exclusionary rule” since 1914 to bar the use of illegally seized evidence.
In 1961, in Mapp v. Ohio, the Supreme Court reversed Ms. Mapp’s conviction and adopted the exclusionary rule as a national standard. The court acknowledged that the rule might let some criminals go free, but it underscored that it was more important to compel the nation’s police forces to obey the law.
The court carved out exceptions over the years, but the basic rule laid down in Mapp has endured for nearly five decades. Now, Chief Justice John Roberts’s conservative majority on the Supreme Court is working to undo the exclusionary rule in a more fundamental way. It’s been a longstanding interest of Mr. Roberts’s. As a young Reagan administration lawyer, he worked on what he described in a memo as a “campaign to amend or abolish” the rule.
The Mapp decision has had both effects that were predicted when it came down. Some criminals had convictions thrown out, or avoided being charged, because evidence was obtained illegally or found by relying on illegally obtained information. But Mapp also changed the incentives for the police. It gave them less reason to enter a home or tap a phone without a warrant.
The exclusionary rule has always had critics. Long before Mapp, Judge Benjamin Cardozo said it allowed the criminal to go free “because the constable has blundered.” In recent years, it has become Exhibit A for those who argue that defendants get off on technicalities.
In 2006, in Hudson v. Michigan, Chief Justice Roberts assigned the majority opinion to Justice Antonin Scalia, who wrote a sweeping assault on the rationale for excluding illegally obtained evidence. Justice Scalia argued that “the increasing professionalism of police forces,” the increased availability of civil rights lawsuits, and other checks on police wrongdoing have sharply reduced the need for such measures.
Last month, the court eroded the rule still further in Herring v. United States. Writing for the majority, Chief Justice Roberts declared that evidence need not necessarily be disqualified if it was illegally obtained because of errors in police databases. Isolated mistakes of this sort, he insisted, are not among the exclusionary rule’s “core concerns.”
Justice Ruth Ginsburg, in dissent, was right to point out that in the modern age database errors can lead to many people’s rights being denied. The harm to a citizen who is arrested and searched on the street because a bureaucrat has made a computer error, she noted, is just the sort of invasion the founders worried about when they drafted the Fourth Amendment.
After Hudson and Herring, critics of the exclusionary rule have high hopes that the Roberts court will take the ultimate step of overruling Mapp v. Ohio. That would be a great setback for the rule of law.
Despite Justice Scalia’s claims, police misconduct is rampant. In the last few years, the Atlanta and Oakland police departments have had major scandals over officers’ lying to obtain search warrants. In this same period, of course, the federal government engaged in an illegal domestic wiretapping program, the extent of which is still unknown.
The exclusionary rule does more than simply put a check on police misconduct. It protects the integrity of the judicial system. If courts put people like Ms. Mapp in prison based on the actions of lawless, marauding police officers, respect for the law suffers.
There is no denying that the exclusionary rule allows a small number of criminals to go free because the police have blundered — which is certainly no minor matter. But the more faithfully the rule is applied, the more likely the police are to collect evidence lawfully.
As important as it is to convict criminals, the Supreme Court in Mapp rightly insisted that the Constitution must not be trampled in the process. “Nothing can destroy a government more quickly,” the court noted, “than its failure to observe its own laws, or worse, its disregard of the charter of its own existence.”