He paths between the area of the Underboss and the Overseer, he is KoS and not on faction, so not only are there no faction hits for killing him but also, no other mobs will assist him.
I have killed him probably 10 times and have gotten the necklace every time. The chestguard is way more rare. Also... this guy has very little HPs. dont know exact amount but probably 1/3 or 1/4 of every other trash mob in zone.