Variola Major
Simply put, the Baron could ONLY have been killed by ground fire. Sorry, Brown, but you didn't shoot him down. No pilot did.
I watched the Nova documentary on that subject. I concur that the forensic evidence placed the killing shot from a machine gun on the ground.
And keep in mind that these were not officially anti-aircraft guns. Just men in the right position at the right time.
von Richthofen was a fool, wounded in the head in prior combat and looking for his death wish that day. Chasing an amateur enemy pilot miles behind enemy lines at roof top level made him an easy mark.