The situation is complicated further by the fact that the user is trying to claim an account that's been involved in suspicious activities in the past.
OK - you stated it - the user is possibly scamming.
You should provide evidence to back this up, otherwise - besides violating any privacy policy you may have ,you look like you are scamming funds.
The thing is, he's trying to claim ownership of an already existing account while writing us from a different email address. We cannot meet him halfway in terms of security and everything we requested is vital.
Sorry if that wasn't clear from our previous replies.