Similar unanswered question, however this question focusing more on where to proceed to now. I am led to believe that there is a bug with Facebook's FQL because the event_member table never returns a non-null answer for "inviter", [tested large and small events, public & private, and self admined events]. There are no reported "inviter" bugs on Facebook's site, and no references elsewhere on the internet. Is it common for Facebook to have an error in their graph ( I should hope not)? Could it be this is now depreciated (With no mark of it's existence)? Should I wait it out or keep trying? If it is a brand new feature of event_member, should there not be a news release etc?
TRY this example on Facebook's FQL explorer: https://developers.facebook.com/tools/explorer?fql=select%20inviter%2C%20inviter_type%2Cuid%2C%20rsvp_status%20from%20event_member%20where%20eid%20%3D%20321938874572158%3B
TL;DR: This doesn't work: Select inviter, inviter_type,uid, rsvp_status from event_member where eid = 321938874572158;