## Facts

- An Illinois state trooper stopped Roy I. Caballes on an interstate highway for speeding.
- While the trooper was writing a warning ticket, a second trooper arrived with a trained narcotics-detection dog after overhearing the stop over the radio.
- The second trooper walked the dog around the exterior of Caballes’s car; the dog alerted at the trunk.
- Officers searched the trunk based on the alert, discovered marijuana, and arrested Caballes.
- The encounter lasted less than 10 minutes.
- Caballes was convicted of a narcotics offense and sentenced to 12 years’ imprisonment and a substantial fine.
- The trial court denied suppression, finding the stop was not unnecessarily prolonged and the alert supplied probable cause; the intermediate appellate court affirmed.
- The Illinois Supreme Court reversed, holding that using the dog without specific and articulable facts suggesting drug activity improperly expanded a routine traffic stop into a drug investigation.

## Issues

1. Whether the Fourth Amendment requires reasonable, articulable suspicion to use a drug-detection dog to sniff a vehicle’s exterior during a lawful traffic stop.
2. Whether conducting a dog sniff during a traffic stop violates the Fourth Amendment when the stop is not prolonged beyond the time reasonably required to complete the traffic mission.

## Decision

- The Supreme Court vacated the Illinois Supreme Court’s judgment and remanded.
- The Court held that a dog sniff conducted during a concededly lawful traffic stop does not violate the Fourth Amendment when it reveals only the presence of contraband and does not prolong the stop.
- The Court emphasized that a lawful traffic stop may become unlawful if extended beyond the time reasonably required to complete the traffic-related tasks, but the state court had not found any prolongation here.

## Legal Principles

- A traffic stop lawful at its inception can violate the Fourth Amendment if executed in a manner that unreasonably extends the seizure.
- A traffic stop justified by issuing a ticket becomes unlawful if prolonged beyond the time reasonably required to complete that mission.
- Use of a well-trained narcotics-detection dog to sniff a vehicle’s exterior during a lawful traffic stop generally is not a Fourth Amendment search when it discloses only the presence or absence of contraband.
- The Fourth Amendment does not require reasonable, articulable suspicion to conduct an exterior dog sniff during a lawful traffic stop, provided the sniff does not add time to the stop.

## Conclusion

The Court held that, during a lawful traffic stop, police may conduct an exterior narcotics-detection dog sniff without reasonable suspicion when the sniff does not prolong the stop and reveals only the presence of contraband, making the state court’s contrary rule invalid under the Fourth Amendment.


Illinois v. Caballes, 543 U.S. 405 (2005)