User blog comment:ScoobycoolDoo/Who's the mole?/@comment-4491822-20111022010051/@comment-1038387-20111102224552

Ra's al Ghul mentions it at the end of Infiltrator (so the Nobody is ruled out). And since that was Artemis's debut, a lot of people fell for what appears to be a red herring.

Unless that double agent stuff mentioned below turns out to be true, we can scratch Artemis off the list.