Hello Richard
I honestly doubt that given the large numbers of fighters engaged in a relatively limited area that it would be possible to identify with any sort of certainty who were the pilots or pilot responsible for the death of Hauptmann von Fassong. My understanding is that he and his wing man were bounced by two P-47 fighters at low altitude and his aircraft went cartwheeling into the ground where it exploded while his wing man was lucky enough to escape with his life. I am including what I have on this ace and any comments or corrections are welcome. I hope that this helps.
http://www.megaupload.com/?d=LQZ1OBNT
Horrido!
Leo