There is nothing from Bittrex because Bittrex probably was not hacked... hacked were email accounts and attackers probably ask for forgot password from bittrex or so. But these mails were probably imediadly deleted because he havent any mails from bittrex in mailbox.
But attackers must knew these mails are connected with bittrex, maybe leaked all emails from bittrex?!?!?
I also think that the victim could be the hacked one, maybe his computer is compromised. Otherwise all other accounts would probably have been hacked too.