DC-ATE said "I have yet to see it in writing just WHO the third crew member was. Have you?"
I, and I suppose hundreds of others have.
From Wikipedia:
"
A total of 128 passengers and seven crew members were on board
[1] when the flight left Istanbul at 6:22 UTC (7:22
CET) under the command of Captain Hasan Tahsin Arısan, one of the airline's most experienced pilots with more than 15,500 hours of flying experience. He had been working for Turkish Airlines since 1996, and previously flew for the
Turkish Air Force.
[9] The other crew members were Olgay Özgür (co-pilot), Murat Sezer (pilot), Figen Eren, Perihan Özden, Ulvi Murat Eskin, and Yasemin Vural."
From samanyoluhaber.com:
KOKPİT: Hasan Tahsin Arısan, Olgay Özgür ve Murat Sezer.
From Yahoo News.com:
Turkish Airlines said the dead included pilots Hasan Tahsin Arisan, Olgay Ozgur and Murat Sezer and flight attendant Ulvi Murat Eskin.