This is interesting. Dotcom does not have great credibility so an assertion is just an assertion. But if it does transpire the DNC e-mails were leaked by a disgruntled staffer, rather than hacked by Russian interests, then that changes the story considerably.
This Herald story reports that Rich was a huge supporter of Sanders and hence could be motivated to expose a pro-Clinton bias in the DNC.
But an assertion and a possible motive is not proof. And stories suggesting Rich was murdered because of this are wildly speculative and have been based on false facts.
But if Dotcom can or does produce alleged proof, or has some specificity to his allegations, then it is worth considering them. But bearing in mind he almost certainly forged the Warners e-mail about John Key, one should be highly sceptical.