Illinois V. Caballes - Majority Opinion

Majority Opinion

The Fourth Amendment guards against "unreasonable searches and seizures." Under the Court's Fourth Amendment jurisprudence, a traffic stop is a "seizure," and requires reasonable suspicion that the driver of the vehicle has violated a traffic law. In this case, it was undisputed that Caballes was speeding. Thus, the traffic stop by itself was lawful from the start.

However, a seizure that is justified at its inception may become unreasonable if it is unreasonably prolonged in duration. Thus, if the sole reason for the stop is to issue a warning to the motorist, the stop becomes unreasonable if it is prolonged beyond the time reasonably necessary to issue the warning. And if a drug-sniffing dog is used during this unreasonable extension, the use of the dog violates the Fourth Amendment. The Illinois Supreme Court reasoned that using the dog changed the character of the encounter from a routine traffic stop to a drug investigation, and that transformation had to be supported by reasonable suspicion. The Supreme Court instead reasoned that the dog sniff does not change the character of an encounter unless the dog sniff invaded any of the citizen's other reasonable expectations of privacy. The Court concluded it did not.

Official conduct that does not invade a reasonable expectation of privacy is not a "search" under the Fourth Amendment. The possession of contraband is not anything in which a person can have a legitimate expectation of privacy, since it is by definition illegal to possess contraband. In United States v. Place, the Court had held that a dog sniff is sui generis because it discloses only the presence or absence of narcotics. By contrast, the information disclosed by the heat sensing device in Kyllo v. United States disclosed the "intimate details in a home, such as at what hour each night the lady of the house takes her daily sauna and bath." People have a reasonable expectation that such information will be kept private, whereas they have no such expectation in the fact they possessed contraband. Thus, the use of a drug-sniffing dog does not intrude upon any reasonable expectation of privacy, and it was not unreasonable for the Illinois police to use the dog during the time it took them to issue a warning to Caballes.

Caballes argued that it was wrong to assume that the barks of drug-sniffing dogs reveal only information regarding the presence or absence of narcotics. But the Court rejected this argument because there was no information before the state courts to support it, and because he did not point to anything else in which a person has a reasonable expectation of privacy that a dog bark might reveal.