I would take the claim of the source given by Assange with a grain of salt. It is really unlikely that someone leaking information obtained by a sophisticated hacking operation would want to draw attention to themselves, their methods and their motives. Attributing it to a disgruntled Sanders supporter is a perfect cover. From the viewpoint of maximizing the damage inflicted, there would be the bonus of sowing distrust within the DNC.
This reminds me of some very successful and damaging WWII deception operations.
Biting the hand that feeds IT
