The RAF credited [Canadian Arthur Roy] Brown with shooting down the Red Baron, but it is now generally agreed that the bullet that hit Richthofen was fired by someone on the ground.[45][51] Richthofen died following an extremely serious and inevitably fatal chest wound from a single bullet, penetrating from the right armpit and resurfacing next to the left nipple. Brown's attack was from above and the left. Even more conclusively, Richthofen could not have continued his pursuit of May for as long as he did (up to two minutes) had this wound come from Brown's guns.[45] Brown himself never spoke much about what happened that day, claiming, "There is no point in me commenting, as the evidence is already out there".

Many sources, including a 1998 article by Geoffrey Miller, a physician and historian of military medicine, and a 2003 U.S. Public Broadcasting Service documentary, have suggested that Sergeant Cedric Popkin was the person most likely to have killed Richthofen.[45][51] Popkin was an anti-aircraft (AA) machine gunner with the Australian 24th Machine Gun Company, and was using a Vickers gun. He fired at Richthofen's aircraft on two occasions: first as the Baron was heading straight at his position, and then at long range from the right. Given the nature of Richthofen's wounds, Popkin was in a position to fire the fatal shot, when the pilot passed him for a second time, on the right.[45][51] Some confusion has been caused by a letter that Popkin wrote, in 1935, to an Australian official historian. It stated Popkin's belief that he had fired the fatal shot as Richthofen flew straight at his position. However, in the latter respect, Popkin was incorrect: the bullet that caused the Baron's death came from the side (see above).

A 2002 Discovery Channel documentary suggests that Gunner W. J. "Snowy" Evans, a Lewis machine gunner with the 53rd Battery, 14th Field Artillery Brigade, Royal Australian Artillery is likely to have killed von Richthofen.[46] However, Miller and the PBS documentary dismiss this theory, because of the angle from which Evans fired at Richthofen.[45][51]

Other sources have suggested that Gunner Robert Buie (also of the 53rd Battery) may have fired the fatal shot. There is little support for this theory.[45][51] Nevertheless, in 2007, a municipality in Sydney recognised Buie as the man who shot down Richthofen, placing a plaque near Buie's former home.[52] Buie, who died in 1964, has never been officially recognised in any other way.