United States v. Place
In United States v. Place, 462 U.S. 696 (1983), the U.S. Supreme Court upheld the use of drug evidence in a criminal case by finding that it was not discovered during a "search" protected by the Fourth Amendment.
In the case federal agents arranged for a narcotics detection dog to sniff a suitcase that they had seized at an airport. The Court noted that "if this investigative procedure is itself a search requiring probable cause, the initial seizure of respondent's luggage for the purpose of subjecting it to the sniff test ... could not be justified on less than probable cause." Id. at 706. The Court held, however, that probable cause was unnecessary, because "the particular course of investigation that the agents intended to pursue here--exposure of respondent's luggage, which was located in a public place, to a trained canine--did not constitute a 'search' within the meaning of the Fourth Amendment." Id. at 707.
The Court reached that conclusion based on an analysis of the particular features of a dog sniff. The Court recognized that "a person possesses a privacy interest in the contents of personal luggage that is protected by the Fourth Amendment." 462 U.S. at 707. But a canine sniff "does not require opening the luggage," it "does not expose noncontraband items that otherwise would remain hidden from public view," and it "discloses only the presence or absence of narcotics, a contraband item." Id. Moreover, it does not cause "the embarrassment and inconvenience entailed in less discriminate and more intrusive investigative methods." Id. Because the canine sniff "is so limited both in the manner in which the information is obtained and in the content of the information revealed by the procedure," the Court concluded that it was not a search under the Fourth Amendment. Id.