This unlikely to ever go trial, so we will really never know. It is a plausible explanation? As a former IT worker the hack explanation seems plausible. When they got hacked, I thought it was either an inside job or incompentent IT staff that that allowed the hack to happen. The indictment seems to point to the latter. In any event, the indictment appears to exonerate the Trump campaign.
I think it was Seth Rich with a flash drive.
He was mad that Hillary stole the nomination from Sanders, and wanted to make sure she did not get elected.