Let's say ...
an authority has collected all privatekeys, e-mail account accesses, passwords ...
and gave it to a person who is now claiming that he is Satoshi.
This 'Satoshi' can ...
Satoshi has mined the first bitcoin block which we also call as genesis block. If real Satoshi wants to identify himself, he can simply use his key to sign a message!
sign a message, make transactions from Satoshi's accounts, send Satoshi e-mails, claim that he is Satoshi.
But he is not the real Satoshi.