Mere evidence rule

In the law of the United States, the mere evidence rule was a historical doctrine that defined the scope of the 4th Amendment to the United States Constitution. The rule was first elucidated in the Supreme Court case of Boyd v. United States.

In Boyd, the Court ruled that a statute that compelled the production of documents, as part of an investigation into the payment of duties, was a violation of the 4th and 5th Amendments. The Court reasoned that the defendant had a superior property right in the papers and that compelling their production as evidence was self-incrimination. The mere evidence rule was solidified in the case of Gouled v. United States, which found that the 4th Amendment only allowed search and seizure of instrumentalities, fruits of the crime, and contraband, but not mere evidence.

A series of cases chipped away at the rule, distinguishing its scope, culminating in the case of Warden, Maryland Penitentiary v. Hayden in which the Supreme Court rejected the rule, saying the it was antiquated and fraught with exceptions. The abandonment of the rule has, however, been criticized; some argue that the rejection of the rule's limitation on searches has led to more intrusive paper searches and less protection for third parties.