1. Why did the Illinois Supreme Court suppress the marijuana found by Trooper Gillette in the trunk of Roy Caballes’s car?
2. Why did the U.S. Supreme Court vacate the Illinois Supreme Court’s judgment?

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.