According to the hacked chat log, David Brock was conspiring with Elliot Fink, Connor Shaw, and Elizabeth Kim, to commit mass murder. He specifically stated that they would 'Seth Rich" upwards of 1000 people who were critical of Hillary Clinton. He is in big trouble.
I think it was leaked by someone in the NSA or another agency that was monitoring them. Probably saved many lives; they seemingly dumped the plan when it was made public. The chat also exposes that it was not Hillary in the debate.