I remember watching a 60s or 70s movie where he gets shot down by a canadian pilot in the RAF
Captain Roy Brown of the RAF did fire on von Richthofen, and got credit for the kill, but...
There was a recent documentary on him where forensics experts went back over the evidence, flight path, eye witnesses, autopsy and such. He was shot from below. They narrowed it down based on who was stationed where on the ground. I'll look for the name...
http://www.pbs.org/wgbh/nova/transcripts/3011_redbaron.html
There is a transcript of the film on this page, with most of the relevent bits near the bottom.
"
NARRATOR: Captain Brown probably fired on von Richthofen from behind and above left. But as the medical reports showed, the Baron was hit by an upward-traveling shot to the right side. After more than eighty years, most of the evidence fails to support Brown's claim. So who did fire the fatal shot?
Ballistics tests can reveal the effect of a bullet fired from different ranges. When a human body is hit there's an explosive effect called hydrostatic shock—the closer the range, the greater the wound damage.
PETER FRANKS (Ballistics Consultant)
: If the bullet had struck von Richthofen at close range, I would have expected a more explosive-type wound. Now the evidence is that the wounds were actually probed by the medical staff after he had been shot down, and they were actually able to follow the bullet
-path through the body.
NARRATOR: A low-damage, low-velocity hit would indicate a long range shot. Moreover, one of the medical orderlies actually found the .303 bullet that had killed the Baron.
PETER FRANKS: The fact that the bullet was found intact inside the clothing of Richthofen is another indicator that it was a long range shot. And I would say that would be probably 600 yards plus.
NARRATOR: Australian Gunners Buie and Evans were in range and could have hit von Richthofen, as they claimed, some 20 or 30 seconds before he is known to have died. But, by their own testimony, they were firing face on to the triplane so they could not have hit von Richthofen on the right hand side.
NORMAN FRANKS: So we asked our gun expert, what do we need to look at? He said, "Have you got somebody who knows what they're doing, 600 yards away, and he's firing at Von Richthofen's right side?" We said "yes." He said, "There's your man."
NARRATOR: Perched on the slope was the Australian gunnery sergeant, Cedric Popkin. He had followed the fight and now swung his Vickers gun through 180 degrees in case the red triplane re-appeared. He was in luck.
NORMAN FRANKS: In our view and final analysis, the best candidate for bringing down von Richthofen was Cedric Popkin, Australian Sergeant machine gunner.
NARRATOR: Though he was their greatest foe, the Allies buried Manfred von Richthofen alongside their own dead on April 22, 1918, with full military honors."