It isn't quite Justice League but it is nice to have a show I can enjoy with my son. We have the most recent episode DVR'd and haven't seen it yet.

With the mind reading Martian Manhunter and M'gann heavily involved with the team as well as the comic world's greatest scheming mind in Batman, my theories on who the mole is boil down to;

The mole is actually a Justice League plant designed to infiltrate their unknown enemies. The mole will gain the Light's trust by feeding them information that appears more damaging then it actually is in an attempt to uncover who they are and what they are intending.

Superboy is unknowingly the mole. His escape from Cadmus was allowed because somehow the Light is able to see and hear through his eyes. The loss of Superboy as a weapon was more than offset by the chance to know what the Justice League is planning.