There was no Fourth Amendment violation where police officers observed appellant late at night at a Goodwill drop station, carrying boxes to his car, and subsequently observed, in plain view, an unregistered sawed-off shotgun when they shone a flashlight into the vehicle. The interaction in this case was voluntary, since Summers was getting the paperwork to prove ownership of the vehicle at the time. Even if the encounter were an investigatory stop, it was justified by the suspicion that Summers had committed, or was about to commit, a crime.