I can sell an account , hop on a VPN and go into my email, provide a screenshot that "another person" logged into my account. No I am not assuming but I'm just saying that the proof you provided is not good enough.
If you could get me the full ip and not a transcripted one I can check whetever it matches one of the users or not. I know you can say they use a VPN but then we're back to what I said earlier that you could have done the same.
Why dont you get the account unlocked, change e-mails and passwords or give the guy a refund?
Why are you keep getting back to the e-mail thing whilst it only takes some time for you to appeal to get the account unlocked ?
Also Staff can see the screenshot you provided, just not the other Members.