I'll ask the obvious question - can you sign a message from the wallet or prove what the balance of coins there are?
Welcome to cryptocurrencies, where the # of coins is publicly viewable. The address (as stated in the original post):
https://etherscan.io/address/0x6966063aa5de1db5c671f3dd699d5abe213ee902There are clearly 8000 coins here. No movement since the ETH ICO, meaning its likely he was an early investor and forgot about his coins until now.