The account was active 1 year ago.

Do you have any proofs of this hack?
We can ask him to sign a message from an old address, so we can be sure before tagging.

Edit: something is very suspicious really. He woke up after 2 of inactivity just to sign a message.
By coincidence, I was the one who verified it.

However, as the account is inactive, there is no reason to tag I guess.