Does the Paladin need to get the killing blow to proc this, or does he simply need to have delt damage (or even a mjaority of the damage) to something before it died?  Since the effect isn't a hard CC fear, and just a debuff, I could see it working either way, obviously if it were an actual Fear CC just plinking something once to proc it would be a bit OP.

Pretty sure you just need to land the killing blow in order to trigger the various paladin on-kill talents. Makes for some interesting tactical gameplay.