it will be better if the account remains locked indefinitely.
Well, case closed. Lol.
Is this a first for a user who can sign a message? Or does it happen more often?
Theoretically, he can, but never did nor did we feel the need to ask for one as it wouldn't have meant much since the private keys seem to have been kept on a possibly compromised email address. There were a lot of question marks that wouldn't have been answered even with the help of a signed message in this case.