Spawns in the southeastern cluster of buildings -- known to spawn in the southernmost building with three citizens, and also the southwest building within that section -- appears on the bottom floor.
Passing thru COB today saw him on track, took him out easily with a 105 bard, 101 mage, 97 wizard + mercs. He dropped the mirror and a Grandiose Handwraps of Alra.
This guy spawns in the SE group of buildings, inside city, I personally only seen him up in the South most building of that section, 3 Citzens inside there, and always on bottom floor.