Police arrested a gunman who was wearing an old-style Boston Bruins goalie’s mask on Saturday afternoon when he allegedly robbed a Keene State College student shortly ­after midnight, prompting the campus to go on lock-down for five hours.

Police said they charged ­Justin Robinson, 22, of Keene, N.H., with one count of armed robbery and one count of reckless conduct. Robinson is not a student at Keene State, a small liberal arts college, police said.