Maryland v. Garrison

Police obtained a valid warrant, based on genuine probable cause and reasonable pre-search investigation, to search what they believed was the only apartment on the third floor of a building — a warrant covering McWebb's unit — but the third floor actually contained a second apartment belonging to Garrison (defendant). Using McWebb's key, officers entered a shared third-floor entryway and began searching Garrison's apartment before realizing the mistake, finding drugs and paraphernalia before stopping the search once the error became apparent. Garrison's motion to suppress that evidence was denied, and Maryland's lower courts upheld the warrant's validity before the state supreme court reversed; the U.S. Supreme Court granted certiorari.