You need to fight the brigand on his ledge. Stepping off his ledge into the water will suicide him. You can fight him when he cons yellow (red if twinked). If you get unlucky, you can step back into sewer water and try again when he spawns. If nothing else, this a good mob to hone skills against higher level with virtually no worry of dying.l
Managed to kill him once before he jumped into the water and suicided. Got nothing special. Really strange though - he spawns in a fairly out of the way spot. You would think there is something special, but considering his low level, it wouolnd't be much.