Ideally they should have a database copy with every user's balance at the time of the shutdown. And every user is associated to e-mail address. This is why I am worried that I did not receive e-mail from them, it is possible that they don't have full or proper DB dump with all affected users.
They can also dig through Mintpal's e-mail service providers (or some email relay system's) logs and extract user e-mail addresses from there. But they would still need balances.
I know its not proof but telling u the balance of btc at that time isnt either (but i know it since i got the po)... Like I said I bought btc thru a dutch company wich still have the record it was done with my bank so my iban is known... Also my email is the same so yes dw about my proof its enough for any police report
You can google the police survey and fill in ur email as 'way to contact u' thats what i have done but the chance u get ur btc back is really small for all of us it is sadly enough But still fill in the survey the more proof they got the better for the case