Illinois v. Caballes

Caballes (defendant) was stopped for a routine traffic violation, and while one trooper wrote a warning ticket, another trooper who overheard the stop on the radio brought a narcotics-detection dog to sniff the car's exterior, all within about ten minutes; the dog alerted to the trunk, leading to a search that uncovered marijuana. The trial court denied Caballes's suppression motion, the appellate court affirmed his conviction, but the Illinois Supreme Court reversed, reasoning the sniff test impermissibly turned an ordinary traffic stop into a drug investigation without individualized suspicion; the U.S. Supreme Court granted certiorari.