With that much money at stake, you seriously need to contact the authorities. Even if a member here knew him/them, that's too big of a situation for someone to take up on their own... Imagine someone going to the door and saying, "Umm, you don't know me, but I know this guy off the internet who says you owe him $7,000... Could you send it back to him, please?"

Hopefully, you get the idea...

Best wishes to you, though.