Weeks v. United States

Justice Day wrote the unanimous opinion of the Court. Day reviewed the history of the Fourth Amendment, noting that it was based on the premise that a man's house was his castle and thus should not be invaded. This feature of the Constitution was written to prevent the kind of general warrants issued by the government in colonial times. Based on the case, Ex parte Jackson, the prohibition against unreasonable searches and seizures was applicable to letters and sealed packages in the mail.

Day quoted Justice Joseph P. Bradley in Boyd v. United States, "It is not the breaking of his doors and rummaging of his drawers that constitutes the essence of the offense; but it is the invasion of his indefeasible right of personal security, personal liberty, and private property." Day noted that the effect of the Fourth Amendment was to place the courts under limitations regarding their power. The courts should not sanction the tendency of law enforcement to obtain convictions by using unlawful seizures. It is the duty of all those in law enforcement to make sure the Fourth Amendment has force.

Day felt that the guarantees of the Fourth Amendment would be useless without the enforcement power of the exclusionary rule. He stated that,

If letters and private documents can thus be seized and held and used in evidence . . . the protection of the Fourth Amendment . . . is of no value and . . . might as well be stricken from the Constitution. The efforts of the courts . . . are not to be aided by the sacrifice of those great principles established by years of endeavor and suffering.

Thus Day placed individual rights before the needs of law enforcement.

Day summed up his opinion by stating that Weeks's letters were taken and not returned, in direct violation of his constitutional rights. Day also noted that "the Fourth Amendment is not directed to individual misconduct of such officials. Its limitations reach the Federal government and its agencies." This statement meant that the exclusionary rule applied only to the federal government and not to states or cities.