It's a piece of the Shadow Archer Set from the Dragon Knight Saga game. "This piece is part of a set worn by the leader of a famous gang of highwaymen who was executed by the Divine Order. Immediately afterwards, the corpse was looted by members of the Aleroth Assassins' Guild. The set was spread throughout the city as brigand after brigand would challenge the wearer of these much-desired pieces to duels in order to obtain them."