Supreme Court of the United States

Illinois v. Roy I. Caballes 

Decided Jan. 24, 2005 – 543 U.S. 405 

Justice STEVENS delivered the opinion of the Court. 

Illinois State Trooper Daniel Gillette stopped respondent for speeding on an interstate highway. When Gillette radioed the police dispatcher to report the stop, a second trooper, Craig Graham, a member of the Illinois State Police Drug Interdiction Team, overheard the transmission and immediately headed for the scene with his narcotics-detection dog. When they arrived, respondent’s car was on the shoulder of the road and respondent was in Gillette’s vehicle. While Gillette was in the process of writing a warning ticket, Graham walked his dog around respondent’s car. The dog alerted at the trunk. Based on that alert, the officers searched the trunk, found marijuana, and arrested respondent. The entire incident lasted less than 10 minutes. 

Respondent was convicted of a narcotics offense and sentenced to 12 years’ imprisonment and a $256,136 fine. The trial judge denied his motion to suppress the seized evidence and to quash his arrest. He held that the officers had not unnecessarily prolonged the stop and that the dog alert was sufficiently reliable to provide probable cause to conduct the search. Although the Appellate Court affirmed, the Illinois Supreme Court reversed, concluding that because the canine sniff was performed without any “‘specific and articulable facts’” to suggest drug activity, the use of the dog “unjustifiably enlarg[ed] the scope of a routine traffic stop into a drug investigation.”  

The question on which we granted certiorari is narrow: “Whether the Fourth Amendment requires reasonable, articulable suspicion to justify using a drug-detection dog to sniff a vehicle during a legitimate traffic stop.” Thus, we proceed on the assumption that the officer conducting the dog sniff had no information about respondent except that he had been stopped for speeding; accordingly, we have omitted any reference to facts about respondent that might have triggered a modicum of suspicion. 

[T]he Illinois Supreme Court held that the initially lawful traffic stop became an unlawful seizure solely as a result of the canine sniff that occurred outside respondent’s stopped car. That is, the court characterized the dog sniff as the cause rather than the consequence of a constitutional violation. In its view, the use of the dog converted the citizen-police encounter from a lawful traffic stop into a drug investigation, and because the shift in purpose was not supported by any reasonable suspicion that respondent possessed narcotics, it was unlawful. In our view, conducting a dog sniff would not change the character of a traffic stop that is lawful at its inception and otherwise executed in a reasonable manner, unless the dog sniff itself infringed respondent’s constitutionally protected interest in privacy. Our cases hold that it did not. 

Official conduct that does not “compromise any legitimate interest in privacy” is not a search subject to the Fourth Amendment. We have held that any interest in possessing contraband cannot be deemed “legitimate,” and thus, governmental conduct that only reveals the possession of contraband “compromises no legitimate privacy interest.” This is because the expectation “that certain facts will not come to the attention of the authorities” is not the same as an interest in “privacy that society is prepared to consider reasonable.” Respondent concedes that “drug sniffs are designed, and if properly conducted are generally likely, to reveal only the presence of contraband.” Although respondent argues that the error rates, particularly the existence of false positives, call into question the premise that drug-detection dogs alert only to contraband, the record contains no evidence or findings that support his argument. Moreover, respondent does not suggest that an erroneous alert, in and of itself, reveals any legitimate private information, and, in this case, the trial judge found that the dog sniff was sufficiently reliable to establish probable cause to conduct a full-blown search of the trunk. 

Accordingly, the use of a well-trained narcotics-detection dog—one that “does not expose noncontraband items that otherwise would remain hidden from public view,” during a lawful traffic stop, generally does not implicate legitimate privacy interests. In this case, the dog sniff was performed on the exterior of respondent’s car while he was lawfully seized for a traffic violation. Any intrusion on respondent’s privacy expectations does not rise to the level of a constitutionally cognizable infringement. 

This conclusion is entirely consistent with our recent decision that the use of a thermal-imaging device to detect the growth of marijuana in a home constituted an unlawful search. Kyllo v. United States, 533 U.S. 27 (2001). Critical to that decision was the fact that the device was capable of detecting lawful activity—in that case, intimate details in a home, such as “at what hour each night the lady of the house takes her daily sauna and bath.” The legitimate expectation that information about perfectly lawful activity will remain private is categorically distinguishable from respondent’s hopes or expectations concerning the nondetection of contraband in the trunk of his car. A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment. 

The judgment of the Illinois Supreme Court is vacated, and the case is remanded for further proceedings not inconsistent with this opinion. 

Justice SOUTER, dissenting. 

I would hold that using the dog for the purposes of determining the presence of marijuana in the car’s trunk was a search unauthorized as an incident of the speeding stop and unjustified on any other ground. I would accordingly affirm the judgment of the Supreme Court of Illinois, and I respectfully dissent. 

At the heart both of Place and the Court’s opinion today is the proposition that sniffs by a trained dog are sui generis because a reaction by the dog in going alert is a response to nothing but the presence of contraband. Hence, the argument goes, because the sniff can only reveal the presence of items devoid of any legal use, the sniff “does not implicate legitimate privacy interests” and is not to be treated as a search. 

The infallible dog, however, is a creature of legal fiction. Although the Supreme Court of Illinois did not get into the sniffing averages of drug dogs, their supposed infallibility is belied by judicial opinions describing well-trained animals sniffing and alerting with less than perfect accuracy, whether owing to errors by their handlers, the limitations of the dogs themselves, or even the pervasive contamination of currency by cocaine. Indeed, a study cited by Illinois in this case for the proposition that dog sniffs are “generally reliable” shows that dogs in artificial testing situations return false positives anywhere from 12.5% to 60% of the time, depending on the length of the search. In practical terms, the evidence is clear that the dog that alerts hundreds of times will be wrong dozens of times.*** 

Justice GINSBURG, with whom Justice SOUTER joins, dissenting. [OMITTED]