Blacke Dickon: "This is the place where Robin Hood was dragged off to from St. Mary's and locked up awaiting the King's pleasure..."
Robin Hood had no rights in society - if you were outside the law you officially did not exist. Anybody could have taken him for a award dead or alive.
However, the Sheriff would have wanted to keep him alive in Nottingham Castle's dungeon until the order to execute him came back from the King.