I don't know who the 'they' are in your question, but yes, it has been revealed who shot down lieutenant commander McCain. He was taken down by an SA-2 (S-75 Dvina) battery with Cpt Nguyễn Lân, commanding, and Lt Nguyễn Xuân Đại, fire control officer; the latter was the one who actually pulled the trigger (or pushed the button, to be precise). The battery was part of the 61st Missile Battalion stationed ca. 12 miles south of Hanoi.