Looking at all the facts, I think the Aussie infantry firing at the plane got him.
The original question was who had "official" credit for the kill, which Allied Command gave to Roy Brown. It has long been disputed, and I have stated directly that it's really anybody's guess as to who really fired the fatal round.
While I, myself, recognize the validity of the claims of ground fire, Allied Command, for some unknown reason, did not, officially awarding the credit to Capt. Brown. There, the matter rests, as far as I know, without a final real resolution, and likely to never be fully resolved to anybody's satisfaction, sans ballistics tests, which are likely to be impossible...
the infowarrior