Zirius said he had something to do before turning himself in. He said that as a result of the curse of an Asmodian witch, he turned into a Worg every night. He can break the curse only if, as a Worg, he bathed in the waters of a nearby spring. You waited until night, Zirius turned into a Worg, and you brought him to the Stalactite Spring. The water there broke the curse.