In Illinois vs. Caballes, 543 U.S. 405 (2005), the United States Supreme Court ruled that law enforcement officers do not need reasonable suspicion to use a drug dog to sniff a vehicle during a legitimate traffic stop.
Roy Caballes was stopped by Daniel Gillette, an Illinois State Trooper, for speeding on Interstate 80 in La Salle County, Illinois. When Gillette radioed the dispatcher to report the traffic stop, a second trooper, Craig Graham, a member of the Illinois State Police Drug Interdiction Team, overheard the transmission and immediately headed to the scene of the traffic stop with his narcotics-detection dog. When Graham arrived at the scene, Caballes’s car was on the shoulder of the road and Caballes was in Gillette’s vehicle. While Gillette was in the process of writing a warning ticket, Graham walked his dog around Caballes’s car. The dog alerted at the trunk. The officers then searched the trunk and found marijuana. Caballes was arrested and charged with trafficking marijuana. It is important to note that the entire incident lasted less than 10 minutes. Although convicted at trial, the Illinois Supreme Court overturned the conviction ruling that a drug dog sniff was unreasonable without evidence of a crime other than speeding.
The United States Supreme Court saw it otherwise. In a 6 to 2 decision, the Court held that the Fourth Amendment is not applicable when law enforcement officers use a drug dog sniff during the course of a legal traffic stop. The Court reasoned that since dog sniffs only identify the presence of illegal items, in which citizens have no legitimate privacy interest, the Fourth Amendment does not apply to their use.
Caballes therefore authorizes law enforcement officers to walk a drug dog around a vehicle during any legitimate traffic stop. If the dog signals that it smells illegal drugs, the officers then have probable cause to conduct a search.