A State Trooper stopped Caballes (D) for speeding. A second trooper immediately headed for the scene with his narcotics-detection dog. D’s car was on the shoulder of the road. The dog was walked around D’s car and alerted at the trunk. The officers searched the trunk, found marijuana, and arrested D. The entire incident lasted less than 10 minutes. D was sentenced to 12 years’ imprisonment and a $256,136 fine. The Appellate Court affirmed, but 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 enlarged the scope of a routine traffic stop into a drug investigation.” The Supreme Court granted certiorari.