Ohio v. Robinette

After stopping Robinette (defendant) for speeding and confirming his license was clean, an officer issued a verbal warning, returned his license, and immediately asked if he had drugs in the car; Robinette said no and consented to a search, which turned up drugs. Robinette argued the search violated the Fourth Amendment because he did not know he was free to leave once his license was returned, and the Ohio Supreme Court agreed, requiring an express advisement that the detainee is free to go; the U.S. Supreme Court granted certiorari.