Vitiare is a thief who can be found in the westernmost gambling tent at the Nashkel Carnival. Upon entering, he will walk towards Gorion's Ward and their party, boldly state that he is a master thief, then steal 100. If one is not quick enough, he can disappear before getting the chance to retake the stolen gold. He won't appear again after the theft.
Arm your party with ranged weapons and enter the tent. Pause the game and direct someone to walk up to Vitiare. Unpause and, when your party member has reached him, he will steal 100 from them. Pause the game again and attack him. Unpause and, if you are quick and effective enough, he will be dead before he can escape.