Assuming his sythe+skype got hacked. http://www.sythe.org/runescape-3-item-exchange/1792310-selling-green-phat-500-mil.html http://www.sythe.org/report-scammer/1792361-scammed-green-phat-500-mil.html#post14256280
You didn't use an official middleman for such a large trade? Also, the mods will tell you to edit in the users profile link into the original post so should do that now.
I know godgenesis personally. Highly doubt he scammed that, the dudes probably making shit up. btw his user ip lookup is interesting.
He didn't have 2FA on sythe, so any hacker could logon to it, so assuming his sythe+skype got hacked.