Johnson v. United States, 333 U.S. 10 (1948), was a significant United States Supreme Court decision addressing search warrants and the Fourth Amendment. In this case, where federal agents had probable cause to search a hotel room but did not obtain a warrant, the Court declared the search was "unreasonable." Johnson is commonly cited for the proposition that the Fourth Amendment creates a "warrant requirement" for searches, and warrantless searches are "per se unreasonable." Background Federal narcotics agents received information that unknown persons were smoking opium in a Seattle hotel. The agents visited the hotel, where they smelled burning opium coming from a room. Without obtaining a warrant, they knocked on the door and were answered by Anne Johnson. The agents arrested Johnson and searched the room, where they found opium and drug paraphernalia. At trial, this evidence was admitted over Johnson's objection, and she was convicted. Johnson appealed, claiming the warrantless search violated her Fourth Amendment rights. The Ninth Circuit affirmed Johnson's conviction. Opinion of the Court In a 5–4 decision, the Supreme Court reversed the Ninth Circuit, ruling that the agents should have obtained a search warrant. Justice Robert Jackson's majority opinion expounded on the importance of warrants, stating they were required by the Fourth Amendment. Justice Jackson described warrants as a judicial check on the executive. Through warrants, he said, inferences are drawn by a "neutral and detached magistrate" rather than by "the officer engaged in the often competitive enterprise of ferreting out crime." If government agents could search dwellings based on their own determination of probable cause, the Fourth Amendment would become a "nullity," leaving the people's security in their homes to "the discretion of police officers." In this case, the strong smell of opium was surely probable cause, meaning the agents would have had no trouble obtaining a warrant if they had applied for one. "No reason [was] offered for not obtaining a search warrant except the inconvenience to the officers," which is certainly "not enough to bypass the constitutional requirement." Justice Jackson, who had recently served as Chief US Prosecutor of Nazi leaders at the Nuremberg trials, noted that the Fourth Amendment separated America, "where officers are under the law," from a police state, "where they are the law." Jackson would revisit this idea the next year in Brinegar v. United States, when he wrote, "Uncontrolled search and seizure is one of the first