Not necessarily. There was likely a lot of brass around that deerstand....some of it no doubt from previous seasons. Investigators should be able to locate the newly spent brass from Willer's rifle and determine how many rounds he fired. I don't see how it could be determined from forensics who fired first though.
forensics can recreate the battle... history channel did it for the battle of little big horn and it was quite interesting...
from the locations of the bodies and the testimony of witnesses, investigators should be able to paint a pretty accurate picture...
for example, if a hunter fired at vang, relatively close miss, the bullet may be lodged in the stand... vang's first shot would be where the bullet came from perhaps... and can be tracked through lasers and such...
watched a lot of csi, but i don't think the investigation will go this far...
teeman